This study investigated the characteristics and differences in Koreans' sense of social isolation across different age groups. In order to achieve this objective, integrated data from five years of the Korea Welfare Panel (KOWEPS) spanning from 2006 to 2018 were analyzed, including the 2nd dataset (2006), 5th dataset (2009), 8th dataset (2012), 11th dataset (2015), and 14th dataset (2018). The sample comprised 57,660 individuals, including 11,314 young people, 15,627 middle-aged people, 13,825 prime-aged people, and 16,894 older adults. Descriptive statistics, frequency analysis, t-tests, one-way batch variance analysis, Scheffe's post-test, and multiple regression analysis were employed for data analysis. The results of this study and discussion are summarized below. First, according to demographic characteristics, single-person households composed of women living alone without a spouse due to bereavement or divorce felt extreme social isolation, especially older adults, low-income households, and economically inactive groups. In addition, self-esteem gradually decreased from youth to old age, and life satisfaction in youth was high in all sub-factors of life satisfaction. Finally, the analysis of the difference in social isolation by life cycle found that the feeling of social isolation intensified from youth to old age. Second, regarding the impact of self-esteem and life satisfaction on social isolation by life cycle, self-esteem and life satisfaction were found to affect social isolation in all life cycles. However, there were differences in factor variables affecting social isolation at each life stage. Third, as a result of examining the effects of self-esteem and life satisfaction on social isolation by period, comparing 2006 and 2018, differences in factors affecting social isolation over time were identified. Based on the above research results, the significance of this study is as follows. First, this study identified negative self-esteem, health status, positive self-esteem, and leisure life satisfaction variables as important variables having the greatest influence by age group. Second, it was empirically confirmed that in our society, high self-esteem, good health, and active leisure activities increased life satisfaction and positive self-perception and reduced the sense of social isolation as an individual actively communicated with society. Third, it is expected that the results of this study and their discussion will be used as basic theoretical data when interest in a happy and healthy life increases after overcoming a period of social isolation. In particular, this study is meaningful in that despite the economic growth of modern society and the improvement of the quality of life, the variables of self-esteem and life satisfaction still play an important role in social isolation.