This study investigated the utilization of Open Educational Resources (OERs) among mathematics teachers in selected public secondary schools in Zambales, Philippines for the school year 2022-2023. A survey was conducted with 75 Junior High School Mathematics teachers to assess OERs usage frequency and extent, identify challenges, examine perceptions of OER's effect on mathematics teaching practices, and propose a development plan for promoting OER utilization. Findings revealed that the typical teacher-respondent was a 33-year-old female with a bachelor's degree, supplemented by master's units, and eight years of teaching experience. They held the position of Teacher III and were familiar with OERs. Respondents sometimes used OERs in their math teaching strategies and disagreed with challenges related to OERs use. They agreed that integrating OERs into mathematics teaching had positive effects. The study observed no significant differences in challenges faced by mathematics teachers when grouped by age, sex, highest educational attainment, years of teaching experience, and teaching position. However, significant differences emerged when grouped by OER knowledge. Likewise, there were no significant differences in perceptions of OER effects when respondents were grouped by profile variables. Furthermore, no significant relationships were found between challenges and OER utilization or between perceptions of OER effects and OER utilization among respondents.