Background: The Five Moments for Medication Safety tool are critical times when a patient's or caregiver's actions can significantly lower the risk of damage linked with their medication(s). Aim: This study aimed to: investigate the effectiveness of nurses' application of the World Healthcare Organization's Five moments for medication safety tool on patients' medication management in long-term care units. Method: an intervention research design was conducted/ A quasi- experimental study with two groups (nurses and patients), and a pre-test and post-test design was conducted. A sample included all nurses who were working in Long-Term Care Units at Alexandria' New Medical Center, Egypt (N= 55) and a proportional sample of 35 patients at Long-Term Care Units. The World Health Organization's Five Moments for Medication Safety tools were used to measure study variables. Results: there were significant differences between patients' and nurses' responses regarding their application of the World Health Organization's five moments for medication safety tool at the two evaluative times of intervention (pre and post) where (P = <0.001*). There was a positive significant correlation between nurses' and patients' outcomes in the overall responses especially in the Second Stage (Taking medication), and Fourth Stage (Reviewing medication) where (p = <0.001*). the intervention had a large effect on the overall patient outcome, with an effect size (of 0.873). Conclusion: When patients are informed about their drugs, encouraged to ask questions, and give good answers, they can play a critical role in minimizing medication errors. Additionally, nurses play a crucial role in medication management by involving, teaching, supporting, and involving all pertinent parties. For them to fulfill this duty, they need to be strengthened by ongoing education and training.