Albert Einstein’s Theory of Special and General Relativity were some of the difficult topics in Physics encountered by the students. Moreover, these topics were taught purely by modular distance learning. This research used a descriptive research design that aims to determine the performance and level of conceptual understanding of Grade 11 students of San Juan Bag-O High School along with identified topics in Physical Science. The data were collected using a teacher-made conceptual understanding test (CUT) and were analyzed using the appropriate statistical tool. At the end of the analysis, the performance of the students on postulates and consequences of both the Special and General Theory of Relativity was satisfactory. For the level of conceptual understanding, it was determined to be a complete understanding of consequences and postulates of the General Theory of Relativity while a partial understanding of consequences and postulates of the Special Theory of Relativity. The findings obtained in this research indicate that Science teachers should make use of modern methods of teaching to improve performance as well as utilize inquiry and interactive teaching to enhance the level of conceptual understanding of the students.