This experiment was carried out on 13 crossbred Ewes divided into 2 groups. Group 1 (n=6) Received no treatment and served as control. Group 2 (n=7) given an oral dose of 0.25 ml the Organic phosphorus compound Selecron for 3 Months. After the end of Selecron administration, both the control and experimental ewes Received half norgestomet ear implant for 12 Days. At implant removal, 800 IU PMSG was inJected i.m. Ewes were monitored for oestrus, Timing to oestrus and duration of oestrus. Ovulation rate was determined on day- 6 post oestrus Using transabdominal ultrasound scanning and Mid-ventral laparotomy. Blood samples were Collected before norgestomet application, before PMSG injection, during oestrus and on day 6- Post oestrus. Serum progesterone level was Measured using RIA. Results indicated that timIng to oestrus was significantly longer (P<0.05) and number of un-ruptured follicles was significantly greater (P<0.05) in Selecron treated group Than control one. Number of corpora lutea (CL) Was significantly greater (P<0.01) in control Than Selecron group. Transabdominal ultrasound Scanning failed to predict ovulation rate in ewes. Serum progesterone level was significantly higher (P<0.01) in Selecron group during oestrus, While, on day- 6 post oestrus it was significantly Higher (P<0.01) in control than Selecron group. Cytogenetical analysis revealed that chronic Exposure of ewes to Selecron pesticide significantly increase (P<0.01) the incidence of total Aberrant cells, chromatid gaps, chromosome Gaps and total structural aberrations. Also, the Incidence of deletion and fragments and chromosome breaks significantly increased (P<0.05) after Selecron administration compared with control group. Non reciprocal translocation 1q 26-20 to 3q terminal part was found in one control ewe. In conclusion, chronic exposure of ewes to the organic phosphorus pesticide, Selecron impair reproductive function as indicated by the signifi- cant decreased in ovulation rate, serum progeste- rone level and marked increase in the incidence of chromosomal abnormalities.