Aim: Investigations on the effect of hypohydration on cognitive function present with ambiguous and contradictory results. The purpose of this study was to evaluate the effect of exertional heat stress induced hypohydration (Graded hypohydration: 2% and 4%) on cognitive function in Human. Methodology: Six healthy military personnel (age: 25__ampersandsignplusmn;4 years, height: 172__ampersandsignplusmn;4cm, weight : 66__ampersandsignplusmn;3 Kg) performed sub-maximal exercise at 45 ?C and 30% Relative Humidity (RH) in Human Climatic Chamber (HCC) till the desired levels of hypohydration were achieved (2% or 4%). Cognition was assessed using stroop color and word test and PGI battery. Result and Conclusion: Cognitive performance was found to be unaltered upon 2% or 4% hypohydration. The cognitive function was retained under hypohydration demonstrating cognitive resilience in response to moderate body fluid deficits (up to 4%).