The movie starts out with Adrian's death and Rocky mourning the anniversary of her death from ovarian cancer. He reminds himself of all that he has went through with her, and they show a Rocky I flashback of the places he saw Adrian (ice rink, pet shop, Rocky's front doorstep.) Pauly is just like he used to be, busting Rocky's balls.
Meanwhile, Mason "The Line" Dixon is an incredible boxer at his prime and he wants competition of his own; something that is really challenging for him.
Rocky, in the mean time, is running his restaurant 'Adrian's.' Rocky's son is dealing with having a father like Rocky because he sees his now 60 signing autographs and he feels he is living in his shadow. Remember that girl that Rocky walked home in Rocky I? She said "Screw you, Creep-O!" Well she is also in Rocky 6, her name is Marie and she is the one you see in the trailer who is living a not so good life and Rocky wants to help her out. Marie has a son named Steps who later stands ringside at the fight.
Rocky feels like boxing again and tries to medical papers saying he can. With a little convincing, he gets them. Paulie loses his job at the meat factory and Rocky hires Marie to work at his restaurantMason "the line" Dixon trains in the mean time and is interested about a computer simulation fight showing Rocky defeating him if the two met in their prime. Two of the promoters come in to talk to him and then go to Rocky's restaurant to ask for him. Rocky is convinced and feels he has a "Beast inside of him" because of all his sorrow when Adrain died .
Rocky's son quits his job and decides to help him train.
Duke, Apollo's old trainer who later trained Rocky, is the trainer in the movie. He tells Rocky to rely on sheer blunt force instead of Apollo Creed like speed. The training scene is intense, especially to see him bring Rocky back into his old form all the time he is 60+. Rocky trains and for a split 3 seconds, you can see Rocky down a shot of eggs, sweet! He even runs up the stairs (but with a dog he got from the pound with Steps). Meanwhile, you see Mason Dixon train.
The fight is located in Las Vegas. Marie gives Rocky a picture of Adrian. They head towards the ring and Mason is there and pulls Rocky and his son aside telling Rocky that he won't embarrass him if he doesn't cheap shot him but if he does he is going to be on the ground. Rocky says "It ain't Over til' it's over." Mason turns his back and leaves and you see Rocky and his son play fighting and back on track again, father- son time.
Coming to the ring Spider Rico sends Rocky a prayer, and Pauly tells him to release his "beast" in the ring and then no more boxing. To the ring the song "Rubber Tree Plant" cover by Frank Sinatra is heard in the background. Then Mason comes out , they hit fists and the fight is on. At first you can notice a difference between all of the Rocky films, it is more like a boxing PPV. Even with a clock at the bottom right of the screen and the angle of a boxing match.
The first round Rocky barely stays up but actually surprises a few people with a blow to Mason's head. Second Round he isn't so lucky and goes down twice. Mason hurts his hand on Rocky, so Rocky takes the chance and beats him down. Mason goes down for a few seconds. From there the Rocky feel starts to kick in, and the music plays and the rounds soar by with punches thrown and blood flying.
Near the last two rounds they focus more on the fight and Rocky punishes Dixon. With a short intermission while he gets hit himself and you hear Rocky's voice in the background to stay up and fight this one last round. Shows flashback to Mickey giving advice and Adrian by the ring, then to Adrian's roses on her headstone. The screen goes black and Rocky is alert and he goes on a rampage on flying fists to Mason Dixon. The bell rings with both still standing and the music playing in the background (fast tempo, like Rocky I.) Marie works her way to the ring while Rocky isn't there to stay.
Rocky gets out of the ring (music still playing) and heads toward the exit with the chanting "ROCKY!" Mason stays in the ring awaiting the count on the split decision. Rocky heads out near the entrance and in the background you hear ".... and the winner, and still undefeated champion, Mason 'The Line' Dixon." Rocky doesn't stop and shakes hand with the crowd. The screen freezes on Rocky shaking a crowd member's hand.
Final shot shows Rocky at Adrian's tombstone saying how far they have gotten. He went all the way and he was happy. Winning wasn't everything he just wanted to prove if you want something go and get it. He puts roses on her tombstone and walks away. He stops for a brief second and you can see him wave.
The screen fades to black and the credits roll.