Novel bi-/tricyclic azasugars fused thiazinan-4-one were conveniently synthesized by the tandem Staudinger/aza-Wittig/cyclization reaction under microwave radiation. The aryl group (phenyl or pyridyl) in mercaptan acid had an important effect on the formation of the diastereomers of the tricyclic hybrids 12b-15b. The new bi/tricyclic azasugars 3a-8a, 4b, 6b, 8b and the known ones 2a, 2b were examined for their HIV reverse transcriptase (RT) inhibitory activities. The result showed that compounds 2a-b, 4a, 4b, 5a, and 6a could effectively inhibit RT activity. Among them, the tricyclic azasugar 5a was the best one with the IC50 value of 0.49 μM. Structure-activity relationship analysis suggested that the phenyl group in the tricyclic azasugars was benefit for their anti-HIV RT activity.