In the present study, 44,440 test day milk yield records, for first lactation of Iranian Holstein cattle, collected between 1983 and 2010 were used to genetic analysis of the lactation persistency of Iranian Holstein cattle with Legendre Polynomials based Random Regression Models. For analysis, animals with 10 test day records were considered and their breeding values for different measures of persistency and 305-days milk yield (305MY) were estimated by Random Regression analysis. Spearman correlations between breeding values of different persistency measures and 305MY were estimated. The correlations between estimated breeding values for different measures of lactation persistency ranged between 0.32 to 0.99. In addition, the correlation between different persistency measures and 305MY varied from 0.35 to 0.99. In general, results showed that because of positive correlations between some measures of persistency with each other as well as with 305MY, these traits could be used to improve lactation persistency and milk production of Iranian Holstein dairy cows