A number of pathogenic microorganisms have been previously shown to bind plasminogen. The subsequent activation of plasminogen into plasmin can contribute to their virulence. In this study, we have shown that Streptococcus mutans is able to bind both human plasminogen and plasmin. Binding of plasminogen to S. mutans was inhibited by l ‐lysine and ε‐aminocaproic acid, indicating that binding is mediated via lysine‐binding sites of plasminogen. S. mutans enhanced the activation of plasminogen by tissue plasminogen activator but not by urokinase. This enhancement turned out to be dependent on cell concentration. Zymogram analysis showed that the plasmin activity acquired after plasminogen binding and activation is the most important proteolytic activity in the strain tested. These results suggest a mechanism involving acquisition of a host protease that might contribute to the infective process of this microorganism.