Membrane type 1 matrix metalloproteinase (MT1-MMP) was suggested to play a critical role in the regulation of tissue invasion by normal and neoplastic cells by directly mediating the activation of pro-gelatinase A. Recently, the proteolytic activation of a pro-MT1-MMP by an intracellular proprotein convertase, furin, was reported. In this study, we found that plasmin efficiently activates the pro-MT1-MMP by cleaving immediately downstream of Arg108 and Arg111 in the multi-basic motif between its pro- and catalytic domains that participates in the activation of pro-gelatinase A. Our present data suggest that pro-MT1-MMP transported to the plasma membrane is activated by plasmin extracellularly and thus it may play an important role in the matrix degradation process.