This study aimed to investigate the correlations among androgen receptor (AR) CAG repeat polymorphism, sex hormones and penile length in healthy Chinese young adult men. Two hundred and iffty-three healthy men (aged 22.8 ± 3.1 years) were enrolled. The individuals were grouped as CAG short (CAGS) if they harbored repeat length of≤20 or as CAG long (CAGL) if their CAG repeat length was>20. Body height/weight, penile length and other parameters were examined and recorded by the speciifed physicians;CAG repeat polymorphism was determined by the polymerase chain reaction (PCR) method;and the serum levels of the sex hormones were detected by radioimmunoassay. Student’s t-test or linear regression analysis was used to assess the associations among AR CAG repeat polymorphism, sex hormones and penile length. This investigation showed that the serum total testosterone (T) level was positively associated with the AR CAG repeat length (P= 0.01); whereas, no signiifcant correlation of T or AR CAG repeat polymorphism with the penile length was found (P= 0.593). Interestingly, an inverse association was observed between serum prolactin (PRL) levels and penile length by linear regression analyses (b=-0.024, P= 0.039, 95%conifdence interval (CI):-0.047, 0). Collectively, this study provides the ifrst evidence that serum PRL, but not T or AR CAG repeat polymorphism, is correlated with penile length in the Han adult population from northwestern China.