Abstract: AIM: To study the effects of prednisone acetate on the histomorphology of rat skeleton. METHODS: 3Monthold male rats were given prednisone acetate (4.5mg·kg^-1) ig, twice a week for 90 days. The proximal tibial metaphysis (PTM), lumber vertebra (LV) and the middle part of tibial shafts (Tx) were processed undecalcified for quantitive bone histomorphometry. RESULTS: PTM: prednisone group vs aging group, trabecular bone loss and poor architecture were found in prednisone acetate treated group. Bone formation indices were decreased and bone resorption perimeter was increased in prednisone group. The change of LV was almost the same as PTM, but the change was less than PTM. TX: The cortical bone and marrow areas of tibial shaft did not change in either the aging control group or the prednisone acetate group during the 90 day experimental period. A decrease in bone formation indices in periosteal surface of Tx in prednisone acetate group was observed. Prednisone acetate markedly increased the percentage of eroded perimeter in the endocortical surface compared with the control group. CONCLUSION: The results show that prednisone acetate has significant effect on the proximal tibial metaphysis, lumber vertebra and the middle part of tibial shafts. These indicate that different part of the bone have different reaction to prednisone acetate.