This study aimed to investigate the effects of nano and organic selenium on ovarian activity, fertility rate, and progesterone hormone levels in Ossimi ewes. Thirty ewes were treated with intra-vaginal sponges impregnated with medroxyprogesterone acetate (40 mg) for 14 d and simultaneously assigned randomly to three groups. The 1st group ewe served as control (CG). Ewes in the 2nd and 3rd groups were treated orally with organic selenium 3 mg/ewe and Nano-selenium 0.2 mg/ewes during intra-vaginal sponges (IVS) treatment SeG and N-SeG, respectively. The ovarian activity was monitored using an ultrasonic device, and serum samples were harvested for progesterone measurement. The results revealed that ewes in SeG and N-SeG groups had a significantly (p