Abstract: Objective To study the damage effects of Microcystin LR(MCLR)on placenta in Sprague-Dawley rats(SD rats).Methods SD rats were injected with MCLR in their embryo forming period to study the effects of MCLR to the placenta and the embryo development.Results Different dose of MCLR can directly injure the placenta barrier and entered into the embryo,which affected the forming and delopment of embryo.The placenta pathological slices showed that there were degeneration,dropsy and interstitium loosen in all placenta cells on the sixth day stopping injection of MCLR.Conclusion MCLR could injure the placenta barrier directly which made MCLR easily enter the embryo and effect the forming and development of embryo.