Older adults are at greater risk of mental health issues. This study examined the factors influencing mental well-being among 2230 Malaysian older adults, using data from the 2018 to 2019 Malaysia Ageing and Retirement Survey. The World Health Organization-Five Well-Being Index (WHO-5) was used to assess mental well-being, and linear regression analysis identified the significant factors. Women had lower mental well-being scores than men (P = .012, β = -0.016). Chinese (P = .024, β = -0.020), Indian (P < .001, β = -0.043), and other ethnicities (P < .001, β = -0.031) reported lower scores than Malays. The factors associated with better well-being were secondary (P = .001, β = 0.032) and tertiary education (P < .001, β = 0.063), and good (P < .001, β = 0.081) and moderate (P < .001, β = 0.038) health status. Diseases-limiting activities were associated with poor well-being (P < .001, β = -0.030). Support from family (P < .001, β = 0.062) and friends (P < .001, β = 0.032), social activity participation (P < .001, β = 0.026), and functional ability (P < .001, β = 0.043) were significant positive factors. There is a need for targeted interventions to enhance mental health among Malaysian older adults.