This study aims to reveal the role of Tanshinone I (TI) in inhibiting osteoclast activity and bone loss in vitro and in vivo, as well as elucidate its underlying molecular mechanism.A mouse model of estrogen deficiency was used to assess the inhibitory effect of TI on osteoclast activity and subsequent bone loss. To validate the impact of TI on osteoclast formation, TRAcP staining and pseudopodia belt staining were conducted. The expressions of osteoclast-specific genes and proteins were evaluated using RT-PCR and Western Blot analyses. Additionally, immunofluorescence staining was employed to examine the effect of TI on p65 nuclear translocation and the expression level of reactive oxygen species (ROS).TI demonstrated significant efficacy in alleviating bone mass loss and suppressing osteoclast activity and function in ovariectomized mice. This outcome was predominantly ascribed to a decrease in ROS levels, thereby impeding the NF-κB signaling pathway and the translocation of p65 to the nucleus. Additionally, TI hindered the RANKL-induced phosphorylation of the MAPK signaling pathway. Moreover, TI played a role in the reduction of osteoclast-specific genes and proteins.To summarize, this study sheds light on TI's capacity to modulate various signaling pathways triggered by RANKL, effectively impeding osteoclast formation and mitigating bone loss resulting from estrogen deficiency. Consequently, TI emerges as a promising therapeutic option for estrogen-deficiency bone loss.Copyright © 2023 Elsevier B.V. All rights reserved.