Executive dysfunction occurs early and is prevalent in Alzheimer's disease (AD). This study tested the ability of different measures for identifying changes in executive function and the effect of 6-months of aerobic exercise on executive function in older adults with mild to moderate AD, using a single-group, repeated-measures design (n = 28, age 78.1 +/- 8.37). Factor analysis and linear mixed-effects model analyses showed that individually the Exit Interview-25 (EXIT-25), Behavioral Dyscontrol Scale (BDS), and Golden Stroop test were the preferred instruments for measuring changes in executive function in the sample. The COWAT and TMT had substantial floor effects limiting their ability to identify changes in executive function. A single latent factor was sufficient to describe the heterogeneity of executive function. Over 6 months, aerobic exercise maintained executive function (effect size = -0.11, -0.24, -0.27, and -0.21 for the EXIT-25, BDS, Stroop, and latent factor, respectively). Decline in the latent factor (effect size = -0.21, p = 0.06) was minimal and comparable to that in global cognition (effect size = -0.20, p = 0.34). Aerobic exercise may be effective on maintaining executive function in AD.