Brazilian cotton crops have been cultivated as a relay crop, sowed late in the planting window.  As a result plants are exposed to drought since squaring, leading to a favorable diminishing of insecticide proteins expressed on Bt cotton plants. Thus, target pests control failures such as cotton bollworm (CBW) can occur. Water stress was studied on growth parameters, as well as on CBW attack and survivorship in Bt cotton. Plants were grown in pots arranged in a 4x2 complete randomized factorial with four replications during the 2013/2014 growing season. Treatments included varieties [FM975WS/Cry1Ac+Cry1F, IMA5675BGIIRRF/Cry1Ac+Cry2Ab, NuOpalBG/Cry1Ac and IMACD6001/non-Bt] and, water regimes (well watered and water stressed). Water stress was imposed at pinhead square stage by reducing irrigation in 70% for three weeks followed by plants infestation with CBW neonates for three days. A foliar disc bioassay was carried out to assess the survivorship of CBW neonates for 96h. Plant growth was reduced on water stressed treatment. Stomatal conductance did not change under drought stressed varieties, but on well watered conditions it was higher on cultivar IMA5675BGIIRRF. Leaf temperature (LT) was not affected by cultivar, nevertheless well watered treatment reduced LT by 0.33 °C. Plant dry weight and reproductive structures number decreased under water stress, but no differences were observed among them. Under stress there is no difference among cultivars on dry weight of a single reproductive structure (RSDW), but with no water limitation the RSDW was increased on cultivars IMACD6001 and IMA5675BGIIRRF. Water stressed plants showed a significant higher number of flower buds with CBW symptoms of attack. The percentage of flower buds attacked was significantly lower in IMA5675BGIIRRF and NuOpalBG varieties. Almost 60% less survivors were observed in the IMA5675BGIIRRF variety after 48h of the infestation. Varieties under stress condition had larval mortality reduced from 30 to 42%.