CXCL2, a member of the CXC family, is involved in various immune and inflammatory processes, while its effects on bone formation have not been reported. We first revealed here that CXCL2 is enriched in bone marrow and further showed abundant CXCL2 expression in osteoblasts of osteoporotic mice. CXCL2 neutralization in the bone marrow alleviated bone loss in the mice, indicating negative role of CXCL2 in bone formation. In line with this, CXCL2 over-expression attenuated proliferation as well as differentiation of osteoblasts in vitro. On the contrary, CXCL2 down-regulation promoted osteoblast expansion and differentiation. Mechanistically, CXCL2 inhibited ERK1/2 signaling in osteoblasts. Activation of ERK1/2 abolished the inhibitory effect of CXCL2 on osteoblasts, while ERK1/2 inactivation reversed the osteogenic role of CXCL2 inhibition. These results proved that CXCL2 attenuates osteoblasts differentiation via inhibiting ERK1/2 signaling pathway. Thus, we demonstrate that CXCL2 is a negative regulator of bone formation and clarify the mechanisms responsible. Pharmaceutical coordination of CXCL2 and the pathways in osteoblasts maybe beneficial in bone formation.