Travolta was the target of two lawsuits earlier this year from two male masseurs who claimed 'Pulp Fiction' star made unwanted sexual advances though they were dropped later.
Alley, who recently revealed that she fell in love with Travolta while working on 1989 movie 'Look Who's Talking, says the actor is not gay.
Asked by talk show host Barbara Walters to comment on persistent rumours about Travolta's sexuality, the actress said: "I know John with all my heart and soul. He's not gay.
"I think in some weird way, in Hollywood, if someone gets big enough and famous enough, and they're not out doing drugs and they're not womanizing, what do you say about them?"
Alley recalls how she fell for both Travolta and actor Patrick Swayze in the 1980s, although she claimed their romances never got physical.
Alley, 61, said she was attracted to Travolta while the pair were making the 1989 movie 'Look Who's Talking,' calling him 'the greatest love of my life.'
"Believe me, it took everything I had inside, outside, whatever, to not run off and marry John and be with John for the rest of my life,' Alley said.
She was in her second marriage at that time and did not want to end it though Travolta was single at that time. The actress later married Kelly Preston, his wife of 20 years.
Alley talks in detail about her love life in her new book 'The Art of Men'.
Talking about Swayze, Alley said, "We did fall in love. I was more willing to break up my marriage and I wasn't willing to break up his marriage," Alley said, explaining why the relationship failed to go further.
