Derivatives of penicillanic acid sulfones are known to be irreversible inhibitors of β-lactamase. Eight 6-tricyclic methylene penicillanic acid sulfones were prepared, and their β-lactamase inhibitory activities were evaluated against β-lactamase types I, II, Ⅲ and IV. Among the tricycles attached to 6-exomethylenepenam sulfones, thiazolobenzimidazole (12a-12b), fluorene (12c), and carbazole (12e), showed inhibitory activity on type I, II and III β-lactamase. But phenanthrene (12d), and anthracene (12f-12h) derivatives showed little β-lactamase inhibitory activity. The synergic effects of the selected compound (l2b) in 1:4 combination with piperacillin showed some protection to piperacillin for the resistant strains of E. coli DC2 and P. aeruginosa 1771.