A pedigree file consisting of 5860 individuals, 167 sires and 1582 dams collected at Makooei sheep breeding station (MSBS) during a period of 24 years (1990 to 2013) was used to calculate the inbreeding coefficients to reveal any probable effects of inbreeding (F) on the studied traits. The studied traits were classified to the five main groups including body weight, KLEIBER RATIO, body measurements, greasy fleece weight and reproductive traits. The inbreeding coefficient among the individuals ranged from 0 to 25% with an average of 0.33%, and ranged from 0 to 25% among the ewes with an average of 0.21%. Fluctuations in individual and maternal inbreeding were observed in the period under study. The average geneRATIOn interval was calculated as 3.6 years. The effective population size of the flock was 51.8 animals. The rate of inbreeding was 0.08% per year and 0.53% per geneRATIOn. Six different models were applied and likelihood RATIO test (LRT) was used to select the appropriate model. Based on the LRT, model II was selected as appropriate model for growth, greasy fleece weight at 6 months of age and KLEIBER RATIO traits. The traits related to the live body weight were affected negatively (P<0.001) by the quadratic individual F. The linear individual regression coefficient of the KLEIBER RATIO was estimated significantly (P<0.01) as 0.001, as well the linear maternal inbreeding regression was estimated significantly (P<0.05) as 0.0002. In general, body measurements were affected negatively by the quadratic effects of inbreeding (both individual and maternal) and positively by the linear effects of inbreeding. The reproductive traits were studied based on ewe inbreeding coefficient. Among the reproductive traits, the quadratic regression coefficient of conception rate was estimated significantly (P<0.05) as -0.22. Quadratic regression coefficient of litter mean weight per lamb born were estimated significantly (P<0.01) as -0.63 per 0.01 change in the ewe inbreeding coefficient. Therefore, inbreeding should be avoided, except for purposes of genetic breeding whose main objective is the fixation of certain alleles in the population.