Objective To explore the effects of Cordyceps sinensis extract (CSE) on osteoporosis and RANKL-mediated osteoclastogenesis. Methods Bone marrow-derived macrophages (BMMs) was isolated from the bone marrow of C57BL/6 mice. CSE was added in osteoclast differentiation. Osteoclasts were stained by tartrate-resistant acid phosphatase (TRAP). The nearly mature osteoclasts were planted on hydroxyapatite plates and the area of bone lacunae was observed by microscope. The F-actin belt was stained by DAPI and phylloeptide and the number of nuclei was observed by confocal microscopy. The expressions of DC-STAMP, ATP6V0D2, TRAP, CTSK, and NFATC1 were detected by q-PCR. The protein expression of the MAPK pathway was detected by Western Blot. The in vivo experiments were carried out by administering CSE to the ovariectomized mice daily through gavage. After 6 weeks of intervention, mouse femurs were taken for morphological analysis. Peripheral blood was taken for ELISA. Results CSE represses osteoclastogenesis, bone resorption, F-actin belts formation, osteoclast specific gene expressions and MAPK signaling pathways in vitro. In vivo study indicated that CSE prevents OVX-induced osteoporosis and preserves bone volume by repressing osteoclast activity and function. It also increases the serum ALP, BGP content, and reduces TRAP content. Conclusion CSE can attenuate osteoclast formation and OVX-induced osteoporosis, suggesting potential clinical therapeutic effects for osteoporosis.