A field experiment was conducted at Irrigation Water Management Research Centre (IWMRC) Belvatagi, Navalgund taluk of Dharwad district under vertisols during kharif 2015-16 to compare surface and sub surface drip irrigation methods in Bt cotton (Gossypium hirsutum L.) with different ETc levels. The experiment was laid out in split plot design with methods of irrigation i.e., surface drip and sub surface drip irrigation as main plots with ETc levels at 1.0, 0.8 and 0.6 as sub plots along with one control (surface irrigation @ 0.6 IW/CPE ratio). Sub surface drip irrigation recorded numerically higher seed cotton yield (3,109 kg ha-1) compared to surface drip irrigation (2,758 kg ha-1). ETc levels did not influence seed cotton yield significantly. Interaction effect of method of irrigation and ETc levels was significant. Sub surface drip irrigation with 1.0 ETc significantly increased plant height (98.08 cm), number of monopodia (3.58), number of sympodia (17.68), total number of bolls per plant (39.03) and seed cotton yield (3,471 kg ha-1). Significantly higher water use efficiency (7.06 kg/ha-mm) was recorded in surface drip irrigation with 1.0 ETc.