A field experiment was conducted from 2009-10 to 2011-12 at Water Management Research Centre Belavatagi, Tq : Navalagund, Dt: Dharwad to find out water requirement and effect of levels of N, P and K fertilization on the performance of Bt cotton (Gossypium hirsutum L.). Experiment was laid out in split plot design with irrigation levels 1.0, 0.8 and 0.6 IW/CPE as main plots and 100,125,150 and 175% RDF levels as sub plots. Bt cotton under 175% RDF recorded significantly increased plant height, monopodial branches, sympodial branches and number of bolls per plant. Application of175% recommended dose of fertilizer recorded significantly higher seed cotton yield than 150,125 and 100% recommended dose of fertilizer. Irrigation levels did not influence seed cotton yield significantly. IW/CPE ratio of 0.8 recorded 22.10 q/ha of seed cotton and was on par with 1.0 IW/CPE ratio (21.88 q/ha) and 0.6 IW/CPE ratio (20.05 q/ha). Significantly higher water use efficiency (3.93 kg/ha-mm) was realized at 175% RDF level and it was at par with 150 % RDF. Water use efficiency was not significant with respect to irrigation treatments. There was increasing trend in total uptake of N, P and K with increasing N, P and K levels of fertilizer application from 100% RDF ( N 81.36 , P 12.12 and K 76.59 kg/ha) to 175% RDF (93.18, P 14.02 and K 82.66 kg/ha). Soil available N, P2O and K2O increased significantly up to the highest level of RDF(175%). However, B:C ratio was 2.27 at 175% RDF/ha and it was at par with 150 % RDF/ha (2.26) and 125% RDF/ha (2.23), but significantly higher than 100% RDF/ha (2.08). So it clearly indicated that 150 % RDF is more beneficial for farmers to get economically good yield. None of the interaction effects were significant, except pooled N uptake.