A series of novel 3-/2,3-substituted pyrido[4,3-e][1,2,4]triazino[3,2-c][1,2,4]thiadiazine 6,6-dioxides 4-28 have been synthesized by the reaction of 3-amino-2-(4-thioxo-1,4-dihydropyridin-3-yl-sulfonyl)guanidine with either 2-oxoalkanoic acids and its esters, or phenylglyoxylic hydrates in glacial acetic acid. Some of them exhibited reasonable or moderate anticancer activity toward human cancer cell