Background: Older adults occupy one third of acute care hospital beds, and the regular duties of many nurses include caring for older patients. A working knowledge of geriatric care competencies is necessary for nurses to provide high-quality care to older patients and their families. It is unclear how nurses who work in acute care hospitals self-evaluate their geriatric care competencies and how these self-evaluated abilities differ from the objective abilities of these nurses. Purposes: This study was designed to explore the geriatric care competencies of nurses in hospitals and to identify the factors associated with these competencies. Methods: This was a cross-sectional study. Nurses who were employed and directly caring for patients aged 65 years and older in any of the adult wards of a medical center located in southern Taiwan were recruited as participants. A structured questionnaire was developed based on a review of the relevant literature and validated using expert consensus. This questionnaire included a demographic datasheet, knowledge of geriatric care scale, attitude of geriatric care scale, self-evaluation of geriatric care competency, and geriatric care competency test. Descriptive and inferential statistics were used to analyze the geriatric care competencies of the participants and related factors. Results: One hundred seventy nurses were enrolled as participants. The average self-evaluation score for geriatric care competency was 67.74 (SD = 0.84). However, the average percentage of correct answers given on the geriatric care competency test was much lower (17.6%). The self-evaluation score was found to be significantly associated with job satisfaction and having received continuing education in geriatric care. In addition, age was shown to significantly affect the percentage of correct answers given on the geriatric care competency test. Conclusions/Implications for Practice: A significant gap was found between the self-perceived and actual competencies of nurses in terms of providing geriatric care. Appropriate policies are necessary to improve the geriatric care competencies of nurses working in hospitals and to oversee the implementation of effective educational methods in Taiwan.