Background Cognition is the collection of an intellectual process, such as perception, thinking, reasoning and remembering for goal-directed behaviors. Recent studies have shown that obesity associated with poor cognitive functions (CFs). However, this association is not known in the Sri Lankan context. The objective was to determine the association of cognitive function and obesity among middle-aged adults in Colombo district, Sri Lanka Methods A comparative cross-sectional study was conducted among 166 middle-aged adults aged 50-60 years in a selected MOH division in Colombo District, Sri Lanka. Generalized and central obesity were determined using the WHO cutoff of Body Mass Index (BMI) and Waist Hip Ratio (WHR) values. CFs were assessed using validated Montreal Cognitive Assessment (MoCA) and Mini Mental State Examination (MMSE) tools. Results The study sample consisted 83 subjects of each obese and normal weight categories while 50% were females. Obese middle-aged adults showed significantly lower CF scores in both MoCA and MMSE compared to the normal-weight adults. In addition, lower MMSE scores were significantly associated with high WHR values. Education level of the obese people was a significant predictor of the cognitive functions. Conclusion Obese middle-aged adults had poor cognition compared with their normal-weight subjects.Therefore, remedial actions need to be taken to overcome adulthood obesity for better neuropsychological functions in the brain.