Aim: We sought to examine the effects of health-care-team-related, patient-related, disease-related, therapy-related, and socioeconomic factors on medication adherence among older adults using a structural-equation-modeling approach. Subject and methods: We examined a hypothetical model based on the World Health Organization’s five-dimensional model of medication adherence among a cluster sample of 593 community-dwelling older adults in Macau. The Chinese versions of the Morisky Four-Item Medication Adherence Scale, Fear of Intimacy with Health Professionals Scale, and the Exercise of Self-care Agency Scale were used to measure medication adherence, professional-help relationship, and self-care abilities, respectively. Results: The structural-equation model indicated that elderly adults that had less than three chronic diseases (β = −0.118, p = 0.015), had taken more medication categories (β = 0.464, p < 0.001), had higher scores of self-care agency (β = 0.160, p = 0.005), higher scores of “willingness to share” (β = 0.111, p = 0.040), and lower scores of “fear of sharing” (β = −0.220, p = 0.001) were significantly associated with better medication adherence. However, marital status (β = 0.031, p = 0.473) was not significantly associated with medication adherence. Overall, the model had good fit to the data (IFI = 0.911, TLI = 0.902, CFI = 0.911, and RMSA = 0.042). Conclusion: Factors related to disease, healthcare team, therapy, and patient were significantly associated with medication adherence among older adults. Developing multifaceted interventions to address the identified factors are necessary to improve medication adherence.