This research examined the effects of the Cry1Ac toxin on the chrysopid predator Chrysoperla externa, fed Ashbya gossypii-aphids reared on cotton (Bt) NuOPAL and non-Bt DeltaOPAL (BollgardTM) for two generations. Individual eggs from the predator were placed in glass containers, and hatched. Each treatment consisted of 20 replicates, each containing one insect. Larvae in treatment 1 were fed A. gossypii individuals reared on a diet of NuOPAL (Bt) cotton leaves. Larvae in treatment 2 were given aphids of the same species previously fed leaves of conventional DeltaOPAL cotton. The average duration of larval instars, pre-pupal and pupal phases from both treatments (Bt and non-Bt) and between generations were evaluated using the t test at 5% probability. The duration of the larval instars in treatment 2 was longer than in treatment 1, but these differences were significant only for the second and third instars. In the second generation, a significant difference in the duration of the first instar and the larval phase were observed. However, when comparing the data on the duration of the second instar, the first generation predators in treatment 1 had a shorter lifespan. The average viability was 96.29% for non-Bt treatment against 91.07% for individuals in the Bt treatment. The results of this study suggests that the biology and development of C. externa larvae fed aphids reared on Bt cotton leaves were not affected by the Bt-toxin, possibly because these aphids do not accumulate the Bt-toxin.