This study aimed to characterise academics' conceptions of teaching in fully online undergraduate distance education courses with no on-campus component. The study aimed to fill a gap in the literature, as previous research had examined conceptions of teaching in face-to-face courses, with a few studies of blended teaching via the Internet in on-campus courses. Fourteen academics from five faculties in a Vietnamese regional university were interviewed, with the study taking place shortly after the outbreak of Covid-19. Grounded theory was used for data analysis. The results revealed four categories of conceptions of online teaching, namely online teaching (1) as transmitting structured knowledge and skills, (2) as guiding students to acquire knowledge and skills, (3) as facilitating students' understanding via interaction and (4) as developing students' understanding and capabilities. The four categories of conceptions were defined and distinguished by a set of six dimensions, which included e-Learning/LMS. The set of categories had some similarities to those found for face-to-face teaching, but also some distinctions which could be explained by the nature of online teaching and learning. The study, therefore, makes a major contribution by establishing a category scheme for conceptions of teaching in online distance education, with detailed characterisation of the four categories of conceptions. The descriptors of the conceptions showed cultural influences, particularly from a Confucian heritage, which is of significance as research into face-to-face conceptions had not found cultural variations.