[Purpose] The present study aimed to investigate the association of phase angle with the continuing activities of residents in a geriatric health service facility for one year. We compared the phase angle among current residents in a geriatric health service facility with those who died within one year. [Participants and Methods] This one-year prospective observational study included 149 residents who entered a geriatric health service facility. We divided participants into two groups: an over one-year survival group and a death within one year group. The receiver operating characteristic curves were created to determine the sensitivity and specificity for predicting one-year mortality based on the phase angle. [Results] The phase angle was significantly higher in the one-year survival group than in the death within one year group and was independently and significantly associated with one-year mortality using binomial logistic regression analysis. The phase angle was shown to have predictive power (based on the area under the receiver operating characteristic curve). Based on the calculation for identifying one-year survival, the optimal cut-off value for the phase angle was 2.95° (area under the receiver operating characteristic curve=0.76, sensitivity 55.6%, specificity 83.3%). [Conclusion] The phase angle may contribute to the prognosis of one-year mortality for residents of geriatric health service facilities.