This study aimed to examine the effect of preparation for old age on the psychological well-being of middle-aged adults and evaluate the serial multiple mediating effects of aging anxiety and perceived stress in the relationship between preparation for old age and psychological well-being based on the perspective of life span development theory that successful accomplishment of developmental tasks affects successful adaptation. A total of 353 middle-aged adults (165 male, 198 female) aged 40 to 65 years completed questionnaires. Results from the analysis using PROCESS macro showed that as the degree of preparation for aging increased also increased the psychological well-being of participants. In addition, the simple and serial mediating effects of aging anxiety and perceived stress were confirmed regarding the relationship between preparation for old age and psychological well-being. This means that the higher the level of preparation for old age of middle-aged adults, the lower the anxiety about aging, which contributes to lowering the perception of stress and as a result, the psychological well-being increases. Results from this study confirm the importance of preparation for old age to improve the psychological well-being of middle-aged adults. Interventions to prepare these adults for old age and increase their psychological well-being should be focused on aging anxiety and perceived stress. Finally, the implications, limitations of this study and follow-up studies are discussed.