The study was conducted to identify the motivating factors of teachers in developing supplementary learning materials in the Schools Division in Central Luzon, Philippines. Findings revealed there were ten (10) motivating factors that help teachers to develop supplementary learning materials namely: helps them to deliver the lesson easier; motivates learners; receives recognition and achievement; promotes participation and ICT collaboration; develops creativity; enhances teaching and learning processes; enhances language, skills and communication; provides contextualized instructional materials; develops skills in writing and drawing; and helps them for ranking purposes. While there were hindering factors why teachers could not develop supplementary learning materials such as: lack of ICT skills and knowledge; lack of time, lack of materials; lack of budget; their teaching loads; additional clerical works; stress; lack of support; no internet connection; and their attitude towards the development of SLMs. Based from the findings of the study, a proposed policy was developed to further improve teachers' motivational factors in developing SLMs and to respond to the issues addressed by the teachers regarding the matter. Conclusions were drawn and recommendations were offered.