Azaphenothiazines are the largest and most perspective group of modified phenothiazines, and they exhibit variety of biological activities. The review sums up the current knowledge on the anticancer activity of isomeric pyridobenzothiazines and dipyridothiazines, which are modified azaphenothiazines with one and two pyridine rings, respectively, against 10 types of cancer cell lines. Some 10-substituted dipyridothiazines and even 10-unsubstituted parent compounds, such as 10H-1,9-diazaphenothiazine and 10H-3,6-diazaphenothiazine, exhibited very potent action with the IC₅₀ values less than 1 µg/mL and 1 µM against selected cancer cell lines. The strength of the anticancer action depends both on the tricyclic ring scaffolds and the substituents at the thiazine nitrogen atom.