Milk records on 639 Holstein cows with first lactation during 1986 to 1991 from Korea Animal Improvement Association were used to estimate genetic parameters and genetic and phenotypic correlations among milk, fat, and protein yields. These records were adjusted to 305 days, two times, and months of calving years. The estimates for heritabilities from multivariate REML were 0.18 and 0.13 for milk yield and fat yield. Also, the heritabilities for milk, fat, and protein yields from multivariate REML were 0.20, 0.286, and 0.572, respectively. The heritability of protein yield was considerably higher than those of other yield traits. The genotypic correlation with milk and protein yield was higher than that of milk and fat yield. The selection index derived from the estimated parameters and economic weight based on the milk price by milk and fat percent was I₁ =3.49X_m + 102.51X_f. Supposing that the price of the differential protein percent were 8 and 9 Won, then, the indices were I₂=-2.22X_m + 2.40X_f + 92.05X_p and I₃=-2.08X_m + 2.26X_f + 86.39X_p, respectively. (X_m=milk yield (㎏), X_f=fat yield (㎏), X_p=protein yield (㎏).