Purpose The purpose of this study was to determine the relationship between sleep quality and cognitive function, depression, and institutionalized elderly activity. The goal is to improve the quality of life through early intervention in the sleeping problems of the elderly hospitalized in the nursing home. Method Twentythree patients who were diagnosed with CDR (clinical dementia grade) 0.5 ~ 2 stages by a psychiatrist from September 3 to 30, 2017 were measured for sleep status, depression, cognitive function and activities of daily living at the same time once a day. The collected data were analyzed using SPSS (v.21, IBM, USA) program. Results The correlation between sleep status and cognitive function, depression, and activities of daily living was not statistically significant, and there was a moderate correlation between cognitive function and depression. Conclusion The results of this study suggest that the development and application of a program that activates the cognitive function that is institutionalized with a positive correlation between cognitive function and depression will be effective in decreasing depression in the elderly patients hospitalized in the nursing home.