Seven compounds (3a–g) of 3,6-bis(substitutedphenyl)-1,4-bis(substitutedphenylsulfonyl)-1,4-dihydro-1,2,4,5-tetrazine were synthesised via reaction of N-arylsulfonyl-α-chloro-substituted phenyl hydrazone and triethyl amine. Their structures were confirmed by IR, 1H NMR, MS, elemental analysis, and 3b was confirmed by single-crystal X-ray diffraction. It was proved they are 1,4-dihydro-s-tetrazine derivatives. The central six-membered ring of 3b has an obvious boat conformation. Their antitumor activities were evaluated in vitro by the SRB method for A-549 cell and the MTT method for P-388 cell. The results show that none of the compounds has good activities, but the substituents have a clear effect on their antitumor activity.