Objective To explore the association between occupational exposure to cesium and sex hormone levels in male workers. Methods A total of 988 male workers involved in assembly work at an electric vehicle assembly plant in Guangdong Province were recruited via purposive sampling. Blood samples of the workers were collected, and blood cesium-133 (Cs-133) levels were determined using inductively coupled plasma-mass spectrometry. Serum levels of estradiol, testosterone, progesterone, follicle-stimulating hormone, luteinizing hormone, and prolactin were measured using chemiluminescence immunoassay. Multiple linear regression analysis was performed to explore the associations between blood Cs-133 and the six sex hormones in the male workers. Results The median blood Cs-133 level was 2.23 μg/L, with a detection rate of 100.0%. Multiple linear regression analysis showed that blood Cs-133 levels were negatively associated with serum estradiol levels (P<0.05), after adjusting for covariates including age, length of service, educational level, marital status, body mass index (BMI), annual household income, alcohol consumption, and smoking. There was no significant interaction between blood Cs-133 levels and age, smoking, alcohol consumption, or BMI in relation to serum estradiol (all P>0.05). Conclusion Occupational exposure to Cs-133 is negatively associated with serum estradiol levels in the male workers of electric vehicle assembly industry, suggesting that occupational cesium exposure may influence male sex hormone profiles.