The purpose of this study was to determine the mediating effect of team member effectiveness on the relationship between principal leadership styles and the professional self-esteem of teachers. Utilizing quantitative, non-experimental design via correlational technique, data were obtained from 300 elementary public school teachers who belong to the 3 districts, Magsaysay, Bansalan, and Matan-ao under the Division of Davao Del Sur. Davao Del Sur. The researcher utilized a stratified random sampling technique and an online survey mode of data collection. The researcher also utilized the statistical tools mean, Pearson r, and Path Analysis. From the results of the study, it was found out that there is a very high level of mean scores for all variables such as team member effectiveness, principal leadership styles, and professional self-esteem of teachers. Also, results revealed that there are significant relationships between principal leadership styles and professional self-esteem, between principal leadership styles and team member effectiveness, and between team member effectiveness and professional self-esteem of teachers. Further, it was revealed that there was a partial mediation effect of team member effectiveness on the relationship between principal leadership styles and the professional self-esteem of teachers.<p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/edu_01/0264/a.php" alt="Hit counter" /></p>