AimTo evaluate the reliability of the ECOEnfSM scale as a tool to assess the professional competencies of Mental Health Nurse Practitioners (MHNP) in their clinical practice. MethodA pilot study, observational, descriptive and cross-sectional, focuses on MHNP who have completed their Specialized Health Training Program (SHTP) in Spain. The data were collected by general and collaborators mentors of the Multiprofessional Teaching Units (MTUs). The Mental Health Nursing Competency Assessment Tool (ECOEnfSM) was used, which consists of three subscales and eight Competence Units (CU). A reliability and validity analysis were conducted (Cronbach's alpha and Spearman's correlation coefficient). ResultsThe Rotation Assessment subscales showed excellent reliability (r > 0.90) with high and very high correlations (r > 0.6) in all UCs with high levels of significance (p <0.01). The Annual Assessment subscale showed good reliability (r > 0.80) with a medium and very high correlation (r > 0.4) with high levels of significance (p <0.01). All UCs showed a good to excellent consistency (r > 0.80). The “Home Visits” assessment criterion showed heterogeneity of data due to there are few MTUs that fully develop it. ConclusionThe ECOEnfSM scale showed very high reliability in MHNP during their training program in Spain. The ECOEnfSM is considered the only objective tool in Spain to assess the professional competencies in this population.