The Wyeast site rates it at 48-58F. I just used this yeast on my first lager 1 week ago and it seemed to either ferment very fast without me noticing or stop fermenting all together when I brought the ambient temp down to about 50F. I plan to take a gravity reading sometime this week, seeing as that's the only real way to tell, but I am a little concerned. I look forward to further input on this yeast from more experienced lager brewers.