The concentration of styrene in air and in blood and mandelic acid in urine were checked for the 60 workers with normal liver function, exposed to styrene. Styrene in air were sampled with personal air sampler at least 4 hours and analyzed by gas chromatography. Blood and spot urine were collected at the end of shift with a vacuum tube and a plyethylene bottle and analyzed by has chromatography and high performance liquid chromatography. Means of air and blood styrene and urine mandelic acid were 8.16 ppm (geometric mean), 0.199 mg/L, and 0.519 g/g creatinine, respectively. The concentration of styrene in air and mandelic acid in urine were high in the FRP factories and low in polymerization factory. Styrene in blood showed large difference by the working process. Styrene in air showed a good correlation with mandelic acid in urine(r=0.6369) and styrene in blood(r=0.6371). The mandelic acid in urine and styrene in blood corresponded to exposure of 50 ppm styrene were 0.890 g/g creatinine and 0.434 mg/L. However, hippuric acid in urine did not show any correlation with styrene in air. Urine mandelic acid excretion expected ratio showed a tendency to decrease according to obesity index and to increase with alcohol consumption.