Aims: We investigated whether the longitudinal relationship between gastrointestinal diseases and subsequent decline in executive functioning over 6 years differed by cognitive reserve. Methods: We analyzed longitudinal data from 897 older adults (mean age 74.33 years) tested on TMT parts A and B in two waves 6 years apart. Participants reported information on education, occupation, leisure activity engagement, and gastrointestinal diseases. Results: There was a significant interaction of gastrointestinal diseases with leisure activity engagement on latent change in executive functioning. Specifically, only for individuals with low (but not those with high) leisure activity engagement, gastrointestinal diseases significantly predicted a steeper subsequent decline in executive functioning across 6 years (i.e., increases in TMT completion time). Conclusion: Cognitive reserve may attenuate the detrimental influences of gastrointestinal diseases on subsequent decline in executive functioning.