In vitro $eta$-lactamase inhibitory activity of 6-exomethylene sulbactam compounds (CH-120, 130, 140, 145, 150, 155) was compared with clavulanic acid, sulbactam and tazobactam. The inhibitory activity of CH-140 was stronger than sulbactam and clavulanic acid against Type II, III, IV, TEM enzymes and stronger than tazobactam against Type IV enzyme. The inhibitory activity of CH-145 was stronger than sulbactam and clavulanic acid against Type I, II, III, IV, TEM enzymes and stronger than tazobactam against Type III, IV enzymes. The in vitro antimicrobial activity of CH-140 and CH-145 combined with piperacillin and ceftriaxone was compared with the sulbactam and tazobactam against $eta$-lactamase producing 31 strains. But, synergistic activity of CH-140 and CH-145 was inferior to tazobactam.