In General purpose polystyrene (GPPS) cups, food is in contact with the articles for a period time and high temperature. Temperature is an important factor in determination of the stability styrene monomer. The migration of styrene monomer into hot drinks may cause chronic toxic effect in nervous system, liver and other organ of body.In this study, 51 samples of hot water (100oC) standing for 60 min were used. Then extraction and distillation of samples were down. Thereafter, 50μl of prepared samples were injected into HPLC (high performance liquid chromatography) for determination of styrene monomer. Calibration of the methods was done by addition of 2.5,5,10,20,30,50 μl styrene working solution to a similar food (hot water) and proceeding with the distillation and extraction. There is linear regression for styrene monomer from 0.25 to 5ng/ml. This method offers a quick, sensitive and reliable procedure for determining of styrene monomer. For the reproducibility of study, styrene monomer was determinated within day and day to day. The results of the recovery study for styrene monomer were ales determinated, and the mean was 94.58% (range 94.31-95.23%). The detection limit is 0.001 mg/kg (1ppb) with the mean of styrene monomer was 7.61±01ng/kg (range 7.07 – 9.56).This study indicated that styrene monomer from polystyrene cups (GPPS) into hot drinks was migrated and this migration highly depended on temperature of water. The concentration of styrene monomer in this study was above the EPA (Environmental protection agency) recommended levels. More study is needed to further elucidate this finding.