The main purpose of this study is to presume the change trajectories in the degree of the social participation and depression of the middle-aged and the elderly and see the longitudinal relations between them as well. The data of KLoSA (Korean Longitudinal Study of Aging: 2006, 2008, and 2010) were used for this study, in which a total of 7,763 middle-aged and elderly people born before 1962 were surveyed, and it was analyzed by the application of latent growth curve modeling. Firstly, as for the change trajectories in the degree of the factors - social participation and depression, the result showed as time passed, the former factor decreased linearly while the latter increased and that the individual difference between them was significant in the change trajectories. On the relationships between each variable, the result showed that in the first year of the research, the higher the level of social participation, the lower depression they suffered from and over the whole period of four years, the higher the social participation, the lower the depression and vice versa as well. The research, which was conducted over the three terms of time, confirmed the change trajectories between social participation and depression and furthermore, studied the relationships between them under the time variation.