The 34-year-old's deal was set to expire at the end of the season, but he has penned fresh terms with the Bundesliga club until June 2016.
Stranzl has proved a popular player at Borussia-Park since joining from Spartak Moscow in January 2011 and has made 130 appearances for Gladbach.
"When the club approached me and asked me if I would sign for another year for me there was not much to think about," Stranzl told the club's official website.
"I feel very comfortable at Borussia and have always said I want to stay here as long as my body allows and the club gives me confidence.
"Therefore I am pleased to be able to play another year for Borussia."
Gladbach have reached the mid-season break in fourth place and will return to Bundesliga action on January 31 at Stuttgart.
