Genetic parameters of milk, protein and fat yield traits in Iranian Holstein dairy cattle were predicted using records gathered in Iran Breeding Centre during 2005 to 2010 across 79 production farms. Information included 276962 test day (TD) records belonged to 30729 primiparous dairy cows. Estimation with the assumption of residual variance homogeneity for whole lactation period was accomplished using restricted maximum likelihood (REML) method in the framework of multiple-trait random regression animal model. Estimated heritability for 305 day milk fat and protein yield showed almost similar results (0.32 to 0.33). For milk yield, predicted heritability as function of days in milk (DIM) resulted in higher value for the middle of DIM than both onset and end of milk production periods. Within traits, estimated correlations for consecutive TD records were higher and with increasing time interval among TD records. It became downwardly lower. Correlations between traits were calculated from covariance components for curve parameters estimated in multi-trait analysis. The range of genetic and permanent environment correlations across traits for 305 day production resulted in 0.76 to 0.93 and 0.87 to 0.97, respectively. The highest and lowest aforementioned parameters were observed among milk protein and milk fat yield, respectively.