Transglutaminase( TGase) from Streptomyces mobaraensis is a kind of cross-linking enzyme which can change the functional properties of protein. During the fermentation of S. mobaraensis,TGase was secreted to the extracellular in the form of Pro-TGase. The Pro-TGase was activated by extracellular metalloprotease and serine protease to form an active TGase. In order to determine which one was the most important protease,two kinds of protease inhibitors( EDTA and PMSF) were added into the media in the process of fermentation. Results showed that TGase activity in fermentation supernatant didn't increase any more when EDTA was supplemented. However,when PMSF was supplemented,the change of TGase activity was not obvious. These results indicated that the metalloprotease is the key enzyme for TGase synthesis.