Abstract The Radio-Based Instruction (RBI) is a learning delivery mode using radio broadcasts to provide modular distance learning. The study determined the extent of implementation and challenges of radio-based instruction among secondary schools in Masinloc District. The descriptive research design using the survey questionnaire was employed in the study. The respondents are females with a mean age of 37.38, married, have earned units in MA/ MS degree, and Teacher 1. The respondents strongly agreed on the extent of implementation and challenges in the implementation of RBI, respectively. There was a significant difference in the extent of implementation of radio-based instruction as to technical requirements when grouped according to the highest educational attainment profile variable. There was no significant difference in the extent of implementation of radio-based instruction when grouped according to sex, age, civil status, and position profile variable. There was a significant difference in the challenges in the implementation of radio-based instruction as to content pedagogy and learning focus when grouped according to sex profile variable. There was a significant difference in the challenges in the implementation of radio-based instruction as to learning engagement when grouped according to the highest educational attainment profile variable. There was no significant difference in the challenges in the implementation of radio-based instruction when grouped according to age, civil status, and position profile variables. There was a negligible relationship between the extent of practices and challenges encountered in the modular distance learning of the respondents. The training programs were developed based on the extent of implementation of RBI. It is recommended that the school head conduct the familiarization and provision of tools used in the implementation of RBI. The USB OTG may be used to facilitate the learning of the students in the RBI. The school head may conduct through an expert on the proper maintenance of the battery-operated AM/FM transistor radios and other modes of radio broadcast to utilize the delivery of RBI. The teachers may encourage the learners to actively participate by asking questions and raising their clarifications during the discussion. The teachers may implement the proposed training programs in the implementation of RBI in Zone 1 of the Division of Zambales, Philippines. Keywords: Implementation, Radio-based Instruction, Modular Distance Learning