The objectives of this study were to investigate the factors affecting interval from calving to first insemination (ICF), genetic and phenotypic relationships among ICF with the fertility and milk yield over 305-d lactation. Besides, the effect of the first insemination after calving on reproductive performance of dairy cows was studied. A total number of 230945 records from 96040 dairy cows from parity 2 to 6 during 1988 to 2017 were analyzed wich have been collected from Vahdat Industrial Agriculturists and Dairymen Cooperative. The factors affecting on interval from calving to first insemination analyzed using GLMM procedure of SAS. Results showed that the factors such as herd-year-month of calving, month of insemination, parity, type of calving, sex of the calves and age at first insemination were significant on the interval from calving to first insemination (p 0.001). Genetic and phenotypic parameters were estimated by animal models based on restricted maximum likelihood (REMEL) using DMU software. The results showed low heritability for reproductive traits (less than 0.1). The heritability of ICF and MY305 was estimated to be 0.11 ± 0.002 and 0.24 ± 0.005 respectively, which were higher than other traits in this study. The genetic correlation between ICF and other reproductive traits varied from -0.41 to 0.70. The lowest and highest genetic correlations between ICF and other reproductive traits were related to INS (0.27 ± 0.02) and CI (0.70 ± 0.03) respectively. The weak phenotypic correlation between ICF and other reproductive traits were observed (less than 0.27). Unfavorable genetic and phenotypic correlations between ICF and MY305 showed the antagonistic correlation between these traits and genetic selection for increased production has led to a decrease in reproductive performance. Genetic and phenotypic trends showed that selection was made to improve milk production and reproductive traits (except ICF) had an unfavorable trend. Favorable trends of ICF indicated improvement of environmental conditions and changes in managerial decisions for the early insemination after calving. The results of the effect of first insemination after calving on reproductive performance showed that ICF had a positive relationship with SF, OD and CI, as well as a negative relationship with INS and IFL. Additionaly, proper reproductive performance was observed in the cows that inseminated at intervals from 61-80 days after calving. Keywords : Interval from calving to first insemination, Genetic and phenotypic analysis, Reproductive performance, Holstein cows.