Reasoning can be fast, automatic, and intuitive or slow, deliberate, and analytical. Use of one cognitive reasoning style over the other has broad implications for beliefs, but differences in cognitive style have not previously been reported in those with mild cognitive impairment (MCI). Here, the cognitive reflection test is used to measure cognitive style in healthy older adults and those with MCI. Those with MCI performed worse than cognitively healthy older adults, indicating they are more likely to engage in intuitive thinking than age-matched adults. This association is reliable after controlling for additional cognitive, self-report, and demographic factors. Across all measures, subjective cognitive decline was the best predictor of cognitive status. A difference in cognitive style represents a novel behavioral marker of MCI, and future work should explore whether this explains a broader pattern of reasoning errors in those with MCI, such as susceptibility to scams or impaired financial reasoning.