Aim: To revel the relationship between porosity, collagen fiber orientation and strengh of theplated bone after rigid plate fixation and removal. Methods: Seventy-two new zealand white rabbitswere used in this experiment. Eight anmals served as control and the other sixty-four were platedon their intact left tibiae with stailess steel (316L) 4-hole plates to induce early osteoporosis. Theplates were removed 2 months after internal fixation in 40 plated animals, 8 of which were sacrificedimmediately following plate removal and the other 32 were killed in successive groups of & each at1,2,3 and 4 months after plate removal. The remaining 24 plated animals were killed at 3,4 and 6months after plate fixation. After sacrifice, the samples of plated bone were prepared for lightmicroscopy, quantitative histological analysis, polarized light microscopy and biomechanical test.Results: The internal fixation with a rigid plate could induce the regional osteoporosis whichmanifested both bone loss and disorganized bone structure (loss of the orientation of the collagenfibers) leading to decreased strength of the plated bone. Although the regional osteoporois couldrecover gradually after plate removal, the bone structure remained disorderly when the bone masshad returned to normal. Delayed restoration of bone structure was related to delayed restoration ofbone strength. Conclusion f Besides the bone loss, the disorganized bone structure is the main causeof decrease of bone strength after rigid plate fixation and removal.