Changes in sex hormonal levels were studied in Schistosoma mansoni infected and praziquantel treated mice (400 x 2 mg/Kg), drug control and in normal control groups. It was observed that schistosomiasis lead to increase in the level of testosterone, progesterone and 17B - esteradiol, 60 and 70 days post- infection in male and female mice, respectively. In praziquantel treated group the level of testosterone was lowered 10, 20 & 30 days post treatment, progesterone and 17 -estradiol fell 30 days post treatment after primary rise. The mechanism of recorded changes will be discussed in details.