This study focused on the effectiveness of Project ARCHIMEDES Video specifically video-lessons on the topics operation on function and solving rational equation and inequalities to students’ mastery in Mathematics of grade 11 students of Union National High School, Academic Year 2023 - 2024. The quasi-experimental research design was employed, and the level of students’ mastery were measured through the researcher-made test. The subjects are two selected sections of grade 11 of Union National High School. One section was the experimental group, and the other was control group. One group was composed of 25 students. The data was analyzed and interpreted using descriptive and inferential data analysis. The level of mastery before using Project ARCHIMEDES is low. On the other hand, the level of mastery in ‘chalk and talk method’ is low. The level of mastery after using Project ARCHIMEDES is very high while the level of mastery in ‘chalk and talk method’ is very high. There is no significant difference on the level of mastery in Mathematics before the exposure to Project ARCHIMEDES and chalk and talk method. There is no significant difference in the level of mastery in mathematics between the two methods before the exposure. There is no significant difference in the level of mastery in mathematics between the two methods after the exposure. However, there is a significant difference the level of mastery in Mathematics of Grade 11students before and after the exposure to Project ARCHIMEDES.