Kellock made his debut in the competition for Edinburgh against London Irish in January 2003, racking up 20 appearances for the capital side before moving to Glasgow in 2006.
"I'd like to congratulate Al Kellock on his 50th appearance," said Warriors head coach Gregor Townsend. "This is a fantastic achievement for someone who gives his all for Glasgow and we're expecting him to lead by example once again."
Recalling his European career to date, Kellock said that the two matches that stood out in his memory were both against four-times winners Toulouse.
"The best one of the lot was the victory over Toulouse in 2009," he said. "That was an amazing game as nobody gave us a chance yet we got three tries to beat them. It was a tremendous moment and a privilege to be involved.
"But my other favourite memory also involves Toulouse when we were stuck there for five days [in 2010] because our kit went missing and a few other things happened that led to the game being postponed. There was an incredible atmosphere in the stadium when the match finally took place. I don't think I have seen any team more keen to beat us as they were incredibly upset at the game being postponed. It didn't bother us and we fed off it. Although we were beaten it was some game."