Effects of phenobarbital on the pharmacokinetics of griseofulvin were studied in rats. Phenobarbital was administered orally for five days at the dose of 75mg/kg/day. Absolute bioavailability of oral griseofulvin was significantly(p<0.005) reduced but total clearance(CL$_s$ was not changed by phenobarbital pretreatment. Absorption rate constant(K$_a$ and maximum plasma concentration(C$_{max}$) were significantly(p<0.05) reduced, and time to reach maximum plasma concentration(T$_{max}$) of griseofulvin was significantly(p<0.05) increased by phenobarbital pretreatment. Changed pharmacokinetics of griseofulvin seemed not to be due to induced enzyme activity by phenobarbital but to reduced GI absorption of griseofulvin.