Aim To ascertain whether vascular smooth muscle cells inhibit vascular smooth muscle cell proliferation by autocrine or paracrine of growth inhibitors. Methods Conditioned medium from rabbit aortic smooth muscle cell was used in this study. The conditioned medium was filtered by cut off M.W. 100 kDa or 10 kDa (Millipore). Smooth muscle cell proliferation was assayed by the measurement of XTT (Boehringer Mannhein). Results Rabbit aortic smooth muscle cell conditioned medium inhibited smooth muscle cell proliferation, 50% smooth muscle cell conditioned medium achieved 45% inhibitory rate of smooth muscle cell proliferation. This inhibition activity substance is dose dependent, 56℃, 30 min heat stable and M.W.less than 10 kDa. Conclusions Rabbit aortic smooth muscle cell could inhibit smooth muscle cell proliferation by autocrine or paracrine growth inhibitors.