This quantitative and qualitative study aimed to figure out the effectiveness of the use of Input-Output concept map in teaching Filipino grammar to the fifth grade pupils of Juan A. Acapulco Elementary School (JAES) Kinuman Sur, Ozamiz City in increasing their mastery level. This study utilized a researcher made Paper-Pencil test (Paragraph and sentence construction as the outputs from the given inputs) to evaluate the pupils' mastery level, pre and post-interviews to the pupils, teachers, and parents, and personal observation done by the researcher to meet the purpose of the study. Results show that using Input-Output concept map in teaching Filipino grammar can effectively promote learning, increase participation, and increase the mastery level of the pupils with the percentage averages of 83.3% and 95.2% for the topics taught, thus, can be added to the teaching strategies of the Filipino teachers.