This study examined the level of happiness and verified the effect of psycho-social factors on happiness of single person households by life cycle. Data from the Wave 2 of the Korean Happiness Study was used. The final sample for the analyses included data from 1,452 adults aged 20 or older who responded as a single-person household and multiple regression analyses were conducted for each life cycle of youth, middle age, and old age. The main results of this study are as follows. The happiness level of all single-person households was found to be average and decreased from youth to old age. In particular, the level of happiness in middle-aged and old age was found to be relatively low compared to youth. In addition, psychosocial factors affecting the happiness of single-person households were different by the life cycle. Satisfaction with standard of living, satisfaction with future stability, depression and social support were common predictive factors that affected the happiness of single-person households in all life cycles. On the other hand, only a sense of safety in youth, trust in others, social equality, self-rated health status, and stress in middle-aged age, and volunteer activities and satisfaction with neighborhood environment and community belonging in old age were the only new predictive factors that affected the happiness of single-person households. Based on this, policy and practical implications for improving the happiness of single-person households were suggested.