Background: Early warning score (EWS) systems have been developed to support ward nurses by aiding in identification of clinical deterioration at earlier stages. Nursing education regarding EWS was expected to reduce the knowledge deficit about the application of the EWS and improve their practice to maintain patient safety. Aim of the study: This study aimed to evaluate the effect of EWS education on nurses' performance regarding identification and response to clinical deterioration. Design: A Quasi experimental research design pre/post intervention was used. Setting: The study sample was recruited from the medical departments affiliated to Ain Shams University Hospital and Mansoura University hospitals. Subjects: Convenient sample of all available nurses (76) working in medical departments affiliated to Ain Shams University Hospital and Mansoura University Hospitals. Tools: I-A nurses self-administered structured questionnaire, II-Nurses' clinical case scenario exam sheet and III-Nurses' Observational Checklist, IV: Nurses' satisfaction scale. Results: There was highly statistically significant increase of the total mean scores of total knowledge  at post-intervention phase compared to pre-intervention phase (t =38.447 & p <0.001). The total mean score of post-test of clinical scenario exam regarding early warning score system indicate highly statistically evident increase of at post-intervention phase as compared to pre-test score (t =62.445 & p <0.001). Also, there is highly significant increase of total satisfactory level of nurses‵ practice at pre - and post-intervention phase (X=18.414 & p <0.001). In addition, 67.1% of the nurses under study reported their satisfaction regarding EWS program. Conclusion: There was significant improvement of studied nurses' performance regarding identification and response to clinical deterioration due to positive effect of EWS educational program intervention. Also, satisfaction concerning EWS educational program was reported sufficiently among studied nurses after program intervention. Recommendations: Nurses' compliance with EWS system and clinical deterioration training should be periodically assessed and validated.