C1q/tumour necrosis factor–related protein‐3 (CTRP3) is a member of CTRP family, and its blood level is reduced in human and rodent models of obesity and diabetes. However, the role of CTRP3 in diabetic nephropathy remains unclear. This study was designed to examine the effects of CTRP3 on cell proliferation and extracellular matrix (ECM) accumulation in human glomerular mesangial cells (MCs) in response to high glucose (HG), and explore the potential molecular mechanisms. Our results demonstrated that the expression of CTRP3 was significantly decreased by HG stimulation in MCs. In addition, CTRP3 overexpression inhibited MCs proliferation, reactive oxygen species level, and ECM production in HG‐stimulated MCs. Mechanistically, CTRP3 overexpression inhibited the activation of the Janus kinase 2/signal transducers and activators of transcription 3 (JAK2/STAT3) pathway in HG‐stimulated MCs. Taken together, these findings indicated that CTRP3 attenuated HG‐induced MC proliferation and ECM production through the inactivation of the JAK2/STAT3 signaling pathway. Thus, CTRP3 may be a potential therapeutic target for the treatment of diabetic nephropathy.