A large number of factors such as osteotropic hormones, cytokines, or growth factors are related to the bone remodeling which is characterized by the coupling of osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Recent investigations have indicated that cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) play a potential role in the bone resorption associated with a variety of pathological conditions such as inflammatory osteolytic disease. Collagen is the most abundant protein of the extracellular matrix of bone, and the participation of collagenase in bone resorption has been widely investigated. In this study, effects of IL-1β and TNF-α on the release of collagenase from osteoblastic cells were measured. The gelatinase activity was also measured by gel substrate analysis (zymography) after electrophoresis of conditioned media of osteoblastic cell culture. IL-1β increased the collagenase activity in ROS17/2.8 and HOS cell culture. TNF-α also increased the collagenase activity of osteoblastic cells. When two kinds of cytokines were treated simultaneously in the culture of osteoblastic cells, synergistic increase of collagenase activity was seen in ROS17/2.8 cells. IL-1β and TNF-α significantly increased the collagenase activity after 6 hour treatment in the osteoblastic cell culture, and there was no additional increase according to the culture period. Osteoblastic cells released the gelatinase and molecular weight of this enzyme was measured about 70 KDa as assessed by zymogram. IL-1β and TNF-α showed increase of the gelatinase activity produced by ROS17/2.8 and HOS cells. Taken together, this study suggested that IL-1β and TNF-α can modulate bone metabolism, at least in part, by increased release of collagenase and gelatinase from osteoblasts.