This study developed and validated decodable reader in Southern Sorsoganon as a supplementary reading material for Grade One pupils at Bulusan Central Sachool, Bulusan District, Division of Sorsogon Province for the school year 2023-2024. The respondents of the study were twenty (20) Grade One pupils. Seventeen (17) pupils were from the last section who took the Modified Comprehensive Rapid Literacy Assessment (mCRLA) for the Beginning of School Year to determine their reading profile, while three (3) Grade One pupils were from the first section who took the field testing since they were identified as At Grade Level/fluent readers. Additionally, five (5) evaluators validated the said supplementary reading material. The study employed ADDIE (Analysis, Design, Development, Implementation, and Evaluation) model instructional design in the development and validation of the material. The decodable reader covered Mother Tongue 1; Quarter 1 under the Most Essential Learning Competencies (MELCs). The validity of the decodable reader was evaluated by evaluators using Evaluation Sheet for Print Resources adopted from DepEd Learning Resource Development and Management (LRMDS) along with the following factors: Content, Format, Presentation and Organization, and Accuracy and Up-to-datedness. The decodable reader in Southern Sorsoganon for Grade One pupils passed DepEd Learning Resource Management and System (LRMDS) standards. Moreover, all evaluators agreed that the material should be approved for use in public schools if the necessary changes and revisions were made. The decodable reader, according to evaluators, would effectively supplement the teaching-learning process for the target pupils. In addition, based on the result of the field testing, the pupils regarded the decodable reader as relatable and interactive reading material.