In this study, bone resorption and bone formation in cortex under the plates of varying stiffness were observed after a single tetracycline labelling was done. The results showed that after plate internal fixation both bone resorption and bone fomation activities were increased with predomination of bone resorption and that enhanced bone remolding appeared a directional development from early endosteal site to middle area of cortex by entering through transverse vessek. The early activated bone remolding in periosteal site extended from the marginal areas of the plate to the center beneath the plate.