This study was carried out to determine the plasma vitamin $D_3$($D_3$) of 3 weeks old broiler chicks (Hubbard line), whose dorsal skin was exposed to different dose of 310 m UV light. The irradiated doses were 0~0.79 J/$ extrm{cm}^2$(6 doses$ imes$5 replica＝30 chicks). The blood samples were collected 2 days after exposure. The lipid in plasma isolated was extracted with ethyl acetate. The $D_3$ was purified by $C_{18}$ cartridge and analyzed by HPLC. The average $D_3$ content in plasma of control chicks was 20 ng /$mell$. When 0.32 J/$ extrm{cm}^2$ of dose was treated, the highest amount of 43 ng /$mell$ was found among those of chicks experimented, corresponding to 2.15 times that of control. However, When more doses than 0.32 J/$ extrm{cm}^2$ were exposed to the skin, D$_3$ contents were decreased gradually. The similar to control level of $D_3$ was observed when 0.79 J/$ extrm{cm}^2$ was applied.