Field trials were conducted in farmers’ fields at Warangal district, Andhra Pradesh, India during 2005-06 and 2006-07 to monitor the population and fruiting body damaged caused by H. armigera in commercially released Bt cotton hybrids under unprotected conditions. In the present study it was found that there was no variability in egg laying among Bt, non Bt hybrids and Narasimha. However, the larval population and fruiting body damage was significantly lower in Bt hybrids than their corresponding non Bt hybrids. Seed cotton yield in Bt cotton hybrids were more than that of non Bt cotton hybrids.