Studies on population dynamics of  pink bollworm  Pectinophora gossypiella (Saunders) in interspecific Bt and non-Bt cotton hybrids was carried out at Agricultural Research Station, Dharwad farm, Dharwad, during 2007-08. The Bt cotton hybrid recorded significantly low percentage of rosette flowers, per cent green boll, locule damage and lesser number of pink bollworm larvae compared to non-Bt cotton. During the peak flowering stage, the percentage of rosette flowers recorded in Bt cotton and non-Bt cotton was 3.33 and 10.86 per cent, respectively. Whereas, 66.60 per cent reduction in pink bollworm larval incidence in and 61.50 per cent reduction boll damage was recorded in Bt cotton over non-Bt cotton hybrid.