Background: Nurses work in ever-changing healthcare environments. Hence, learning plays a key role in their professional development and continuous improvement of patient care.

Aim: This study aimed to assess the effect of Work-Based Training (WBT) on mental health nurses' clinical competence.

Research design: A one-group quasi-experimental design with pre-post assessment was used in carrying out this study.

Setting: The study was conducted at Abbass-Helmy Center for mental health and addiction treatment affiliated to the General Secretariat of Mental Health and Addiction Treatment. Subjects: All available staff nurses (n=50) were included in this study. Tools: Data were collected by using two tools, namely a self-administered questionnaire for nurses’ knowledge, and a clinical competency observation checklist.

Results: of The study revealed that nurses in the study age ranged between 25 and 59 years, median 29.0 years, with the majority being females (92.0%), and having a diploma degree nurses (84.0%) also there was unsatisfactory knowledge of clinical competence before the implementation of the intervention while post-intervention phase there were statistically significant improvements in almost all areas of knowledge reaching to 100.0% and percentage of nurses who had adequate competencies increased from 18.0% before the intervention to 44.0% after the intervention.

Conclusion: The study findings concluded that there was statistically significant weak to moderate positive correlations between most nurses’ post-intervention scores of knowledge areas and their total competencies.

Recommendations: Competency -based training programs must be provided to nurses in various levels at different health settings to improve their skills and knowledge. And the curriculum of nursing students should contain competency-based training in nursing care of psychiatric patient to improve their competencies.