Urban streets are important public spaces for daily activities that play a crucial role in promoting health in the elderly. The purpose of this study was to investigate the association between perceived street walkability and mood in the elderly, and specifically, the mediating effect of environmental preference and place attachment. We surveyed a total of 269 elderly residents from six streets in Guangzhou, China. We collected assessments of the street environments, environmental preferences, place attachment, and mood status from the elderly. A serial multiple mediator model was constructed using the structural equation modeling method. The results showed that the perceived street walkability was sequentially associated first with an increased level of place attachment (β = 0.798, SE = 0.358, p < 0.000) and then environmental preference (β = 0.191, SE = 0.033, p = 0.038), which was in turn related to improvement of positive mood in the elderly (β = 0.595 SE = 0.341, p < 0.000). Environmental preference alone was found to be significantly associated with positive mood (β = 0.595, SE = 0.341, p < 0.000), while no significant effect of place attachment was found when considered individually (β = −0.075, SE = 0.089, p = 0.395). These findings provide a greater understanding of the possible mechanism through which street environment impacts mood in the elderly. Therefore, when promoting the emotional experience of the elderly, we might consider not only physical environment factors but also psychological conditions in street environments.