Police and a lawyer for Sage Stallone, 36, the younger of two sons from his father's first marriage, gave conflicting accounts of how he was found, but police said there was no sign of forced entry or foul play.
Los Angeles police spokesman Lieutenant Andy Neiman said police found the younger Stallone's body in the home while responding to a call asking authorities to check on his well-being. He said the case was turned over to the county coroner's office.
Attorney George Braunstein said he was found by a housekeeper.
"There was some concern that his family and friends hadn't heard from him in the past day, and that's why the housekeeper went over there and opened up the house," the lawyer said. "It's a tragedy. He was a young, talented extremely good filmmaker and a lovely person."
Sage Stallone had appeared in a number of films, most notably with his father in 1990's "Rocky V," playing the title character's son, Rocky Balboa Jr., and in the 1996 disaster movie "Daylight," in which Sylvester Stallone starred as a hero leading an escape from a New York tunnel collapse and his son played a prison inmate.
Sage Stallone was the second of two sons fathered by Sylvester Stallone, now 66, with his first wife, Sasha Czack, whom he divorced in 1985 after about 10 years of marriage. He has three other children by his third and current wife, Jennifer Flavin.
A statement issued by the elder actor's publicist said: "Sylvester Stallone is devastated and grief-stricken over the sudden loss of his son, Sage Stallone. His compassion and thoughts are with Sage's mother, Sasha. Sage was a very talented and wonderful young man. His loss will be felt forever."
Neither police nor Braunstein had any specifics about the circumstances of the death.
"We don't know any of the details but it must have been some sort of tragic accident. He was full of life and working on projects," Braunstein said. "He wasn't at all depressed or anything like that."
Braunstein said he believed that Sylvester Stallone was returning to Los Angeles from the Comic-Con pop culture convention in San Diego.