Stemtuberlines A (1) and B (2), two new alkaloids with a unique tricyclic pyrrolo [3,2,1-jk]benzazepine-12-one nucleus, three new croomine-type alkaloids, stemtuberlines C-E (3-5), together with seven known ones were isolated from the roots of Stemona tuberosa. The structures of the new alkaloids were elucidated based on a comprehensive spectroscopic data analysis. The absolute configurations of 1 and 2 were determined by quantum ECD calculations. The anti-tobacco mosaic virus activity of the Stemona alkaloids was firstly evaluated and compound 11 exhibited significant anti-tobacco mosaic virus activity with the curative inhibition rate of 84.6% at concentration of 50 mu g/mL.