Cluvulanic acid and sulbactam have been widely used in Japan as beta-lactamase inhibitors, and we will soon have tazobactam, the third beta-lactamase inhibitor. It will be available in combination with piperacillin(1:4), and expected excellent clinical efficacy in various infection, caused by class A, class D and class C beta-lactamase producing bacteria, including ESBLs producing gram negatives. The clinical usefulness of tazobactam/piperacillin might be exceeded those of drugs which combined with cluvulanic acid and sulbactam. However, it dose not inhibit class B beta-lactamase and large amount of class C beta-lactamase. There are some reports of newer beta-lactamase inhibitors, which show much more strong activities against class C or even against class B beta-lactamase in fundamental studies. Continuous studies will be needed to these agent for the future clinical use.