Background Nurses’ knowledge and attitude regarding the care of older people can have an impact on patient outcomes such as reduced length of hospital stays, reduced readmission rates, and increased patient and family satisfaction. However, evidence is scarce in Ethiopia, particularly in the study area. Therefore, the study aimed to assess the knowledge, attitude, and associated factors towards the care of older people among nurses working at public hospitals in West Shoa Zone, Ethiopia. Methods Institutional based cross-sectional study was conducted from April1–30, 2021 among 423 nurses who were working in adult care units. Data were collected through a self-administered questionnaire. The sample was selected using simple random sampling. The logistic regression analysis model was fitted and the Adjusted Odds Ratio at 95% confidence interval was used. P-values less than or equal to 0.05 were considered statistically significant. Results A total of 411 nurses participated in the study with a 97.16% response rate. The mean age of the participants was 29.11 (SD ± 3.84) years. The study showed that 37.2% (95% CI: 33, 42%) of the participants had good knowledge and 45.7% (95% CI: 40.9, 50.6%) had a favorable attitude toward the care of older people. The significantly associated factors positively affected both the knowledge and the attitude of nurses. Age greater than 30 years (AOR:2.37, 95% CI: 1.18, 4.75), experience greater than 5 years (3.00: 1.21, 7.41), being BSc degree holder and above (3.57: 1.40, 9.09), lived with older people (2.14: 1.34, 3.42), and nurses working in adult intensive care unit (3.03: 1.03, 8.91) were significantly associated with knowledge. Likewise, being female (2.04: 1.33, 3.12), being BSc degree holder and above (2.77: 1.35, 5.65), lived with older people (1.59: 1.03, 2.44), and care for older people (1.63: 1.06, 2.53) were significantly associated with attitude. Conclusion In this study, less than half of the nurses had good knowledge and a favorable attitude towards the care of older people. Continuous professional development regarding the care of older people is important to enhance nurses’ knowledge and attitude.