The surfaces of the spin-coated polystyrene (PS) on glass were modified by carbon negative-ion implantation with various ion doses from 1x10(14) - 3x10(16) ions/cm(2) at various ion energies from 5 - 20 keV through a pattering mask slits of 50-mu m. width to investigate the neurite outgrowth properties. After 2-day in vitro culture of the nerve-like cells of rat adrenal pheochromocytoma (PC 12h) on the C-implanted PS films, as well as on type-I collagen-coated dish as a reference, with the serum medium, the culture medium were changed to the serum free medium with a 50-ng/ml nerve growth factor (NGF) and the cells were cultured for observation of the differentiation in cell body and the neurite outgrowth. After 2-day culture in the serum fire medium with NGF, results show that the neurite lengths on the surface of the PS implanted with around 2-3 (x10(15)) ions/cm(2), corresponding to the optimum decreasing of contact angle, can be comparable to that of the surfaces of coated by type-I collagen.