The main objective of the present study was to estimate the persistency of lactation in Sahiwal cows using different persistency indices and to estimate heritability of persistency. Data on 808 Sahiwal cows maintained at the Livestock Experiment Station (LES), Jahangirabad, District Khanewal were used for the present study. Persistency of lactation was determined using five indices viz. Wood, Johnson and Hansen, Mahadevan, Ludwick amd Petersen and Gajbhiye and Tripathi. Statistical model included fixed effects of period and season of calving and parity and random factors of animal. Indices values for Wood, Johnson and Hansen, Mahadevan, Ludwick and Petersen and Gajbhiye and Tripathi were 138.66, 75.68, 243.65, 85.84 and 275.41, respectively. Moreover, our results indicated that all indices were significantly affected by period and season of calving and lactation number except that Wood index that did not vary with seasons. Heritability estimates of various indices were low and ranged from 0.004 to 0.067 indicating very lower genetic control. This is the first study to show genetic of persistency of lactation. Although results may be validated using more data and more accurately recorded pedigree for several generations however, this is really useful firsthand information.