Older adults are not actively participating in outdoor physical activities. An understanding of what factors influence older adults’ outdoor physical activities is important for informing interventions. This study aims to examine the potential effect of service ontology on the intention of outdoor physical activities in older adults. Face-to-face surveys were conducted with 421 older adults from eight districts in Nanjing, China. One-way analysis of variance and ordinal logistic regression analysis revealed that seven of the 20 factors have a positive effect on intention of outdoor physical activities, including gender, health self-assessment, family structure, accessibility, exercise instructors, emergency service, and staff in outdoor space. To further improve the intention of outdoor physical activities, governments and service designers should focus on providing age-friendly community infrastructures. Moreover, specific attention should be paid toward older females and people with low-income/poor health conditions, and strategies should also be adopted to significantly improve the quantity and instruction efficiency of exercise instructors.