Obesity is an established risk factor for cognitive impairment. Theories of cognitive reserve suggest that premorbid factors, such as intellectual ability, may attenuate the expression of cognitive impairment due to age or disease. The current study examined whether cognitive reserve, defined as estimated premorbid intellectual ability, moderates the relationship between obesity and cognitive function in obese adults. Participants without major medical or psychological conditions completed a computerized battery of neuropsychological tests. Hierarchical regression models found a significant interaction between BMI and cognitive reserve for attention/executive function and memory, suggesting that cognitive reserve attenuates the expression of obesity-related cognitive impairment.