This study determined the relationship between teacher professional development and teacher assessment practices among private school teachers in Panabo City. It specifically examined the extent of teacher professional development in terms of planning, executing, and evaluating, and the extent of teacher assessment practices in terms of verification assessment, facilitative assessment, praise, functionality of assessment, and structure of assessment. A quantitative descriptive-correlational research design was employed. The respondents consisted of 172 private high school teachers selected using Slovin’s formula from a total population of 298. Data were gathered through adapted and validated survey questionnaires. Statistical tools used included weighted mean, Pearson product-moment correlation, and multiple regression analysis at a 0.05 level of significance. Findings revealed that both teacher professional development and teacher assessment practices were at an extensive level, indicating that these practices were oftentimes evident among teachers. A significant relationship was found between teacher professional development and teacher assessment practices, suggesting that improvements in professional development correspond to enhanced assessment practices. Moreover, the domains of planning, executing, and evaluating significantly influenced teacher assessment practices, with planning emerging as the strongest predictor. Based on the findings, it is recommended that school administrators and education officials strengthen professional development programs by focusing on structured planning, effective execution, and continuous evaluation. Teachers are also encouraged to actively engage in professional development initiatives to further improve their assessment strategies and instructional effectiveness.