This study examined the feasibility and effect on aerobic fitness of a 1-yr, twice-weekly, group-based moderate-intensity walking program (MI-WP, n = 77) compared with a low-intensity activity program (LI-AP, n = 75) for community-dwelling older adults with mild cognitive impairment (MCI). Thirty participants did not start a program; median attendance in the other 122 participants was 71%. Small but significant associations were observed between attendance and memory in the MI-WP and general cognition in the LI-AP. Associations were no longer significant when both groups were analyzed together. Intensity, assessed using percentage of heart-rate reserve and the Borg scale, equaled intended intensity for both programs. Aerobic fitness improved significantly in participants in the MI-WP. In conclusion, cognition was not clearly associated with attendance in the 62 participants starting the MI-WP, and average attendance was good. The intensity was feasible for participants who continued the MI-WP. The findings support the proposal that regular moderate-intensity walking improves aerobic fitness in adults with MCI.