"It's a dream come true for Sheldon when he has a close encounter with his hero, Mr. Spock," a synopsis said.
Nimoy's voice will be heard as his iconic "Star Trek" character in the March 29 episode of the show.
"For this episode, we are delighted to hear his voice. We look forward to introducing Mr. Nimoy, body part by body part, over the course of many seasons to come," Executive Producer Bill Prady said in a statement.
Currently in its fifth season, "The Big Bang Theory" stars Jim Parsons and Johnny Galecki as Sheldon and Leonard, a pair of brilliant physicists whose lives are turned upside down when a free-spirited beauty, played by Kaley Cuoco, moves in next door.