This animation film tells us about an elderly widower named Carl Fredricksen and a young Wilderness Explorer named Russell who fly to South America by floating in a house. Carl Fredricksen was a shy and quiet boy when he was young. He idolizes a famous explorer named Charles F. Muntz. But Muntz has been accused of fabricating the skeleton of a giant bird he had claimed to have discovered in Paradise Falls, Venezuela, South America. Muntz vows to return there to capture it one alive.
One day, young Carl befriends with an energetic and eccentric tomboy named Ellie, who is also a Muntz’s fan. She confides to Carl her desire to move her "clubhouse" ( an abandoned house ) to a cliff near Paradise Falls. Ellie makes him promise to help her. And, time goes on, Carl and Ellie eventually get married and grow old together in the restored house. They work as a toy balloon vendor and a zookeeper. Unfortunately, they are unable to have children. So, they repeatedly save their salary for a trip to Paradise Falls, but end up spending it on more pressing needs. An elderly Carl finally arranges for the trip, but someday Ellie becomes ill. And, she dies, leaving elderly Carl alone.
Time passed, Carl still lives in that house. It is surrounded by urban development now, but he always refuses to sell. One day, he injures a construction worker because he has damaged Carl’s mailbox. Next day, he is evicted from the house ( because of injuring worker ), but they ( the construction workers ) deem him a public menace that Carl is ordered to move to aretirement home. However, Carl still wants to keep his promise to Ellie. So, he turns his house into a makeshift airship by using thousands of helium balloons to lift it off its foundation. And, accidentally, a young member of the Wilderness Explorer named Russell becomes an accidental passenger. It is because of pestering Carl to earn his final merit badge for Assisting the Elderly.
After surviving from a thunderstorm, the house lands near a large ravine in the area of Paradise Falls. Carl and Russell begin to walk around the ravine by fastening the house’s hook on their bodies. They hope they will reach the falls before the balloons deflate. Later, they befriend with a tall and colorful flightless bird named Kevin which is trying to reach her chicks, and also a dog named Dug who wears a special collar that allows it to speak.
Carl and Russell unexpectedly meet some dogs which are led by Alpha, and they are taken to Dug's master, who turns out to be an elderly Charles Muntz. Muntz explains that he has spent many years since his disgrace at searching Paradise Falls for the giant bird. When Russell innocently reveals his friendship with Kevin, Muntz becomes hostile of Kevin, the giant bird which difficultly he looks for. And, of course, it prompts Carl, Russell, Kevin and Dug to flee, but Muntz successfully chase them by his dogs. Muntz does a fire beneath to Carl's house. He forces Carl to choose between saving his home or Kevin. Carl rushes to put out the fire, allowing Muntz to take the bird. Carl and Russell eventually reach the falls, but Russell is angry with Carl.
At Carl’s home, Carl looks very sad reminiscently Elli’s childhood scrapbook. He finds photos of their married life and a final note from Ellie who is thanking him for the " adventure " and encouraging him to go on a new one. And then, he goes to find Russell, only to see him sailing off on some balloons to save Kevin. Carl empties the house of his furniture in order to re-float it and pursues Russel soon.
Unluckily, Russell is captured by Muntz, but Carl manages to board the dirigible in flight and free both Russell and Kevin. Muntz pursues them around the airship. Dug, Kevin, and Russell are cornering inside Carl's tethered house. Carl lures Kevin out through a window and back onto the airship with Dug and Russell clinging to Kevin’s back. Muntz leaps after them, but unfortunately he falls to his death. And, the house keep floating through the clouds. Carl accepts it as being for the best.
Carl, Russell and Dug reunite Kevin with her chicks. Then they begin to fly the dirigible back to the United States. After they comeback to the United States, Carl proudly presents Russell with his final badge for assisting the elderly. And then, they look enjoying some ice cream together, sitting on the curb outside the shop as Russell and his father used to do, with the dirigible parked near them. Meanwhile, Carl's house is shown to have landed on the cliff beside Paradise Falls, as his promise to Ellie. The end.