Histologic investigations have demonstrated that root canal sealers can induce mild to severe inflammatory alternations. However, there is little information on the precise mechanisms about root canal sealer–induced inflammatory reaction. The proteolysis of extracellular matrix by matrix metalloproteinases (MMPs) and plasminogen activators (PAs) seems to be a key initiating event for the progression of the inflammatory process. The aim of this study was to investigate the effects of epoxy resin–based root canal sealer AH26 and zinc oxide–eugenol–based root canal sealer Canals and one paste sealer N2 on the expression of MMPs and PAs in human osteoblastic cell line U2OS cells. The levels of gelatinolytic and caseinolytic activities were measured by gelatin and casein zymography. The results showed that AH26, Canals, and N2 were cytotoxic to U2OS cells in a concentration-dependent manner (P < .05). The gelatin zymograms revealed that MMP-2 (72 kd) and MMP-9 (92 kd) were secreted by U2OS cells. The exposure of U2OS cells to root canal sealers resulted in the up-regulation of MMP-2 and MMP-9 expression (P < .05). Casein zymography exhibited a caseinolytic band with a molecular weight of 70 kd, indicative of the presence of tissue type plasminogen activators (t-PA). t-PA was also found to be up-regulated by root canal sealers (P < .05). Taken together, the activation of gelatinases and t-PA might play an important role in the pathogenesis of root canal sealer–induced periapical inflammation.