Abstract: ［Abstract］Objective　To investigate the effect of osteoporosis on tibia articular cartilage of SD rats，and the relationship between estrogen and the degeneration of articular cartilage．Methods　Forty eight-month old SD rats were divided into two groups randomly，one was experiment group，another was control group．Three month later， we got the osteoporosis model successfully. Then the rats were sacrificed at 2 th， 4 th， 8 th， 12 th week．The gross pathology and the immunohistochemistry of collagen，I，Ⅱ，III and sox9 were measured．Results　HE staining showed that the number of chondrocytes and cartilage thickness were similar in experiment and control group at 2 th，4 th week．Meanwhile joint surface was smooth and tide lines were integrated．Compared with control group，cartilage thickness became thinner（P＜0.05），and the joint surface was locally destroyed in experiment group at 8 th week．Also，tide lines were integrated and the number of chondrocytes were similar．At 12 th week， cartilage thickness were distinctly thinner（P＜0.05），the number chondrocytes increased remarkably，joint surface became rough and denudations appeared，tide lines were not integrated in experiment group. Immunohistochemistry staining showed the expression of collagenⅡdecreased sharply at 8 th and 12 th week，the expression of sox9 had no obvious change．Compared with experiment group，Mankin’s grade scale of control group was significantly decreased（P＜0.05）at 8 th，12 th week. Conclusion　Osteoporosis can affect the articular cartilage structurally，the decrease of estrogen can lead to degeneration of articular cartilage in rats.