The 53-year-old actor plays cowboy Woody in the animated film franchise. He wasn`t expecting to find the experience as challenging as shooting a live action film, and was shocked by how emotional he found many of the scenes.
In one particularly poignant musical montage in the second film in the series, Tom and his co-star Tim Allen, who plays Buzz Lightyear, were reduced to tears.
"In the scene set to When Somebody Loved Me, I was in tears, and we were looking at each other going, `That`s some powerful stuff,-" Tom revealed.
"So to be reduced to that and to a level of emotion like that on a cartoon about talking toys and their adventures, it`s profound - there`s no other word for it."
"It`s embarrassing, Tom, is what it is," Tim joked. "Grown men weeping."
Tom and Tim reprise their roles in Toy Story 3, which is due for release later this month. Tom says he still has trouble believing he is involved in such a successful franchise, even though it had been 15 years since he starred in the first one.
"It is a profoundly moving and special experience," he told ET Online. "Look, we make a lot of things, and we see them for the first time - by and large it kind of works; maybe it works, maybe it doesn`t, but the three Toy Story movies we`ve seen, every time I`ve come out of there I`ve just slapped my head and said, `I can`t believe I`m a part of this.`"