The purpose of this study was to assess the effectiveness of 12 months of walking exercise interventions to improve sleep quality in older adults. One-hundred ninety healthy older adults were divided into a 12 months walking exercise group (n = 120) and a control group (n = 70). Furthermore, to investigate whether the difference in step count changes affected sleep quality, the walking exercise group was sub-divided into a high-walking exercise group (n = 60) and a low-walking exercise group (n = 60) according to the median number of percent change of steps. The main outcome measures were daytime sleepiness (Epworth Sleepiness Scale: ESS) and sleep quality (Pittsburgh Sleep Quality Index: PSQI) questionnaires. The high-walking exercise group showed significant improvements in ESS (p < 0.01), PSQI global score (p < 0.01), subjective sleep quality (p < 0.05), sleep disturbance (p < 0.05) compared to the baseline scores. In the high-walking exercise group, the result of average step counts per day was significantly increased compared to the baseline (p < 0.01). These results suggest that the 12 months walking exercise intervention was an effective approach to improve sleep quality in older adults who maintained the increase in step counts during the intervention period.