['To investigate the inhibitory effect of testosterone on oxidized low-density lipoproteins (ox-LDL)-stimulated phenotypic transition and proliferation of vascular smooth muscle cells (VSMCs) in vitro, and explore its possible mechanisms.', 'Rat VSMCs were cultured using serum starvation method to make cell synchronization. Cells in vitro were divided into control group, ox-LDL group (treated with 50 μg/mL ox-LDL), FBS group (treated with 100 mL/L fetal bovine serum), and testosterone groups (treated respectively with 5×10(-8) and 5×10(-7) mol/L testosterone for 12 hours, followed by incubation with 50 μg/mL ox-LDL). The effect of testosterone on the ox-LDL-induced proliferation of VSMCs was explored by WST-1 assay. The cell cycle distribution was determined using flow cytometry. Western blotting was used to detect the expressions of mitofusin 2 (Mfn2), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), proliferating cell nuclear antigen (PCNA), α-smooth muscle actin (α-SMA) and osteopontin (OPN).', 'Compared with control group, the proliferation of VSMCs was promoted by ox-LDL, the number of VSMCs decreased in G0/G1 phase and increased in S phase significantly, the expression levels of Mfn2 and α-SMA were significant reduced, and the expression levels of p-ERK1/2, PCNA and OPN were significant raised in ox-LDL group. Compared with ox-LDL group, testosterone showed stronger inhibitory effect on the proliferation of VSMCs induced by ox-LDL, arrested most of the cells in the G0/G1 phase, ascended significantly the expression levels of Mfn2 and α-SMA, and descended significantly the expression levels of p-ERK1/2, PCNA and OPN in the two testosterone groups in a slight dose-dependent manner.'] Does [ Testosterone suppress oxidized low-density lipoprotein-induced vascular smooth muscle cell phenotypic transition and proliferation ]?