This study examined the developmental trajectories of perceived level of stress and depression in Korean youth using longitudinal data from the Korean Youth Panel Study (KYPS) of 2,844youth (1,524 boys) across $4^{th}$ grade through $8^{th}$ grade. Latent growth modeling indicated the presence of age-related, significant increases in stress and depression for both boys and girls. Girls experienced greater in stress and depression than did boys. Multiple group analysis indicated that there was no significant sex difference in effects of stress on depression. Overall, increases in stress were associated with increases in depression levels for both boys and girls. Conceptual and clinical implications of the findings were discussed.