Lung cancer has been the first cause of death for a long time in Taiwan. Smoking is considered as the primary carcinogen, but the smoking rate of female is even lower in Taiwan. Epidemiology research shows that cooking oil fume is the significant risk factor of lung cancer. Restaurant workers are study subjects of this research. There were 46 waiters, 59 cooks and 20 vendors recruited to join this study. Urine samples of pre-work and post-work were collected. We use tt-DDE (trans, trans-2,4-decadienal) to represent the exposure of cooking oil fume. Cooks and Vendors used personal air sampling equipment to collect the tt-DDE while they were working. We wanted to develop an LC-MS/MS analysis method for simultaneously quantification of urinary 8-OHdG and cotinine. To monitor the oxidative stress after the exposure of cooking oil fume. The simultaneously analysis method for quantification of urinary 8-OHdG and Cotinine has been established. Quantification range of cotinine is from 0.5ng/mL to 1000 ng/mL. The limit of detection (LOD) is 0.5ng/mL. Accuracy is from -0.22% to 3.76%. Precision is from 0.86% to 7.67%. The quantification range of 8-OHdG is from 0.5ng/mL to 15ng/mL. the limit of detection (LOD) is 0.5ng/mL. Accuracy is from -2.28% to 0.19%. Precision is from 1.42% to 8.24%. R2 values are larger than 0.995. Urinary 8-OHdG concentrations of cooks and vendors are higher than waiters (p-value <0.0001) and urinary 8-OHdG concentrations of post-work are higher than of pre-work. Urinary cotinine concentrations of cooks and vendors are also higher than waiters.( p-value<0.0001)