The shape of the lactation curve of cows as well as the total or 305 day milk yield is considered as an important criterion in the livestock farms. Five different. mathematical models. used in defining lactation curves were used in this study to fit first loci at ion curves of Holstein cattle. Total of 4172 weekly average milk yield of the first lactation of 104 cows between 2001-2008 years, was used for this aim. The models used in the study were; Wood; Morgan; tlompertz; Ali and Schaeffer and Dijkstra. The models' fit to t h e lactation curve has been examined and compared. Lactation curves also have been investigated according to the lactation years. The R-2, R-adj(2), AIC, BIC and MAPE values were used in the comparison of the models. The lowest AIC (-3.29), BIC (-3.12) and MAPE (0.55) and highest R-2 (0.99) and R-adj(2) (0.99) values were found for the Ali and Schaeffer model. This model was followed by the Dijkstra model. As a result of the study, it was determined that the most suitable models fir predicting the first lactation milk yield curves and curves features like maximum milk yield and days in milk to peak yield of Holstein cattle were Ali and Schaeffer and Dijkstra models.