To investigate effects of cultured astrocytes from Sprague Dawley rat cerebral cortex on the development of PC12 cellsderived from rat pheochromocytoma, PC12 cells were cocultured with astrocyte according to different astrocytes/neurons ratio(50:1～1:1) , or with serum-free conditioned medium of astrocytes(ACM). The vitality of PC12 cells was measured by sensi-tive MTT method and their morphologic features were observed by Olympus light microscope. The results showed: (1) WhenPC12 cells were cultured with ACM, compared with the control group, the vitality of PC12 cells was increased significantly (0.255+0. 012 vs 0. 510±0. 036, P<0. 001) and the morphological changes were not obvious in the experimental group. (2) WhenPC12 cells were cocultured with astrocyte in the ratio of 30: 1～1: 1, not only was the vitality of PC12 cells enhanced, but alsothe neurite-outgrowth of PC12 was observed. (3) When PC12 cells were cocuhured with astrocyte in proportion of 50: 10～40 : 1, the vitality of PC12 cells was also enhanced, but the neurite-outgrowth of PC12 was not found. This study suggested en-hancement of PC12 cell-vitality was mediated by soluble factors produced by astrocytes, while activity of the neurite-promotingwas associated with cell-cell contact and with the ratio of two cells.