Quantitative determination of urinary mandelic acid (MA) phenylglyoxylic acid (PGA) and hippuric acid (HA) (metabolites of styrene monomer.) was conducted. For the determination of urinary MA and PGA, a known amount of myristric acid (internal standard) is added to the urine, before its extraction with mixture of ethyl acetate and ethyl ether. After evaporation of the solvents, the acids are silylated with bis (trimethylsilyl) acetamide. For the determination of urinary HA, HA in ethyl acetate extract from urine, is methylated with diazomethane. Thereafter they were injected into gas chromatograph. Rats were administrated styrene intraperitoneally, and their urins were collected as time lapses. Maximum excretion of MA and PGA reached after 24 hours from styrene injection and that of HA did after 6 hours. Total excretion of MA was caluculated to be 45.9% of styrene administrated that of PGA 23.9%, that of 18.1% and that of all metabolites 87.9%, respectively. Discussion was made between amount of styrene exposed with people and amount of their urinary metabolites.