Microlearning-based lessons are still new in the field of education because it primarily focuses on corporate training and adult learning. Hence, limited research was conducted in basic education even in higher education. Microlearning-based lessons are designed and delivered in the form of small, bite-sized information which allows students to achieve a certain learning objective. The main purpose of this research is to determine the effectiveness of Microlearning-based Lessons in Chemistry in the level of academic performance of 18 (...) Grade 9 students under the online learning modality. Moreover, the research instrument used was a researcher-made pretest-posttest based on the learning competencies of the Most Essential Learning Competency (MELC) consisting of 25 multiple choice items along the topics in Grade 9 Chemistry during the Second Quarter of the school year 2020-2021. Mean and paired t-tests were used as tools for analysis. Findings reveal that students’ exposure to Microlearning-based Lessons in Teaching Grade 9 Chemistry improved their level of academic performance in Chemistry. This implies that students perform better when they use microlearning-based lessons in learning Chemistry. Thus, it can be concluded that the level of performance in Chemistry of Grade 9 students greatly improved after exposure to microlearning-based lessons. Furthermore, this shows the effectiveness of the intervention material in improving their level of academic performance, thus the microlearning-based lessons be adopted in teaching Chemistry is recommended. (shrink)