The study on the effectiveness of teaching and learning mathematics online focused on teachers' perspectives on the experiences they face in real-life situations in the Nepalese context. This study examines the effectiveness of online mathematics teaching and learning in higher education during the COVID-19 pandemic. It is based on a qualitative exploratory case study design. The results of the study are based on the holistic views of eight persistently selected university mathematics teachers. It examines the effectiveness of teaching mathematics online covering four areas; teacher preparation and technological competence, the issue concerning students, access to resources, and the nature of mathematics. Teachers' technical competence and preparation for online lessons were rated as satisfactory. Similarly, student-related issues were found to be uncooperative and dependent on teacher guidance during online learning. Likewise, students were found to benefit according to their access to resources. Urban students have an advantage in online learning over remote students. Similarly, the results suggest that online math classes were perceived as difficult due to the nature of mathematics. Thus, the study concludes that higher-level online mathematics education has several determinants that make online mathematics education effective compared to face-to-face classroom instruction.