This study was designed to investigate the effect of chronic and acute heat stress on sex hormones level and their relationship to sexual puberty in male rats. Used 45 male pups in the age of weaning, were randomly divided for 3 groups each group included 15 pups of each sex. 1st group was a control group, 2nd group exposed to chronic heat stress at 38Cº for 1hour a day since the age of weaning until onset of puberty and the 3rd group exposed to acute heat stress at 38Cº for 4 hours per day for 5 consecutive days from 35 day age of rat and each group above were secondarily divided into 3 age groups consisted of pre-puberty, at puberty and post-puberty. Results of study showed that male rats exposed chronic heat stress led to a significant increase in body weight, tail of epididymis, prostate gland weights, at onset of puberty compared with control group, with a significant decrease in body weight, testis, head and tail of epididymis, prostate and seminal vesicle weights at post-puberty compared with control group. as well as a significant decrease in the level of luteinizing hormone at post-puberty compared with acute heat stress group. Males exposed to acute heat stress cause a significant decrease in the head and tail of the epididymis, prostate, and seminal vesicle weights and significant increase in the concentration each of testosterone and luteinizing hormones at post-puberty compared with the control group. Acute exposure to heat stress caused early sexual puberty in males to show from the early appearance of first sperm compared with the control group, while the exposure to chronic heat stress led to delay of puberty associated with a delay in the appearance of first sperm compared with the control group. It concluded from this study that male rat's exposure to heat stress affects differently on sex hormone. Acute heat stress led to reach early sexual puberty and reflected the impact on puberty when chronic exposure to heat stress.