Hymenolepis nana is one of the commonest parasites worldwide especially in children. Praziquantel was the most effective drug in hymenolepiasis treatment, but with the risk of resistan- ce development. There was a need for search for drug(s) to overcome this problem. Tamoxifen (an estrogen-receptor modulator), is available, low cost with potential anti-parasitic efficacy. This study assessed the therapeutic effect of tamoxifen drug on mice experimentally infected mice with H. nana at different developmental stages. Clean laboratory bred mice infected with H. nana eggs were divided into 4 groups according to different schedule of tamoxifen administration (20mg/kg body weight) at the parasite different developmental stages and control one (infected non treated). At the experimental mice were sacrificed and parasitological evaluated for worm burden count, their weight, egg count and viability. The results did not show statistically significant effect on worm burden as compared to control one, with the exception of mice treated two days post-infection that showed significant increase in worm burden. There was significant decrease in worm weight, egg count and viability as compared to control ones, but without difference between different treated groups.