The aim of this experiment is to study the effects of antithyroid agent (Propylthiouracil, PTU) on domestic chicks male reproductive system. 36 local male one day old chicks were used. Chicks were distributed randomly to three groups, first group (control group) fed standard diet, while 2nd and 3 rd groups were fed diet contain 0.01 and 0.1 % of antithyroid agent (Propylthiouracil PTU) respectively, from 1 - 25 days of age. Chicks were killed at the end of 4th week in order to study the effects of PTU treatment on some male reproductive system and secondary sexual characteristic as well as some body organs. Results revealed that PTU treatment significantly decreased body weight, significantly increased right and left testis percentage and absolute weights in group treated with 0.1% PTU compared with the control group. Treatment also significantly increase comb length and height as well as in liver and heart weights.