The actor and his castmates filmed the final episode last month (April 2019), and Johnny returned to the set to clean out his things and say a last goodbye to his TV home for the past 12 years.
And on Wednesday, he posted an emotional video to Instagram showing set being torn down.
Walking around the empty rooms on the Warner Brothers lot in Burbank, California, Galecki offered fans the chance to see what has become of the set.
He also visited his old dressing room and showed off a series of cardboard cutouts of himself and his castmates.
"Moving out of my @bigbangtheory_cbs dressing room..." he captioned the video.
The final episode will air in America next week, May 16, and Galecki, who plays Leonard Hofstadter on the comedy show, and his co-star Kaley Cuoco will present a look-back special, "Unraveling The Mystery: A Big Bang Farewell", after it ends.
"The Big Bang Theory" began in 2007 and both Galecki and Cuoco have been there for the duration. During their time on the show they dated, while Kaley has since wed twice and Johnny recently announced that he is expecting his first child with girlfriend Alaina Meyer.
"We are absolutely over the moon to announce that we will soon be welcoming a little one into this crazy and wonderful world," the parents to be announced in a statement last month (April 2019). "We ask that you please respect our privacy during this celebratory time for us and our families. There truly is love out there for all. We hope ours is the ember of yours, as we feel yours is the ember of ours."