Many universities in the U.S. shifted from in-person teaching to online teaching due to the COVID-19 pandemic. Instructors' acceptance of online teaching plays a crucial role, as the acceptance level can impact instructors' online teaching behaviors. This qualitative study examined medicine and public health instructors' perceptions of online teaching using the Technology Acceptance Model 2 (TAM2) model. Through semi-structured interviews with ten instructors in a Midwest university in the U.S., this study found that instructors had a high level of acceptance of online teaching. Instructors perceived the usefulness of online teaching in terms of learning objectives, assessment, instructional methods, and learning experience. Online teaching was perceived as useful overall, although challenges existed, such as online interaction, assessment, and hands-on practices. Regarding ease of use in online teaching, instructors perceived technology was easy to use; yet some pedagogical challenges existed, such as class engagement, the focus of learners' attention, and transforming hands-on lab or clinical sessions online. The blended model is recommended to use for teaching and learning in medical and public health education post the pandemic. Detailed implications for practice and research were discussed in the end.