During the course of screening for antibiotics, Streptomyces sp. A271 ATCC 31358 was isolated from soil collected near Eiheiji Temple in the Yoshida District of Fukui Prefecture and was found to produce a new β-lactam antibiotic which we designate as PS-5. The antibiotic was found to have good inhibitory activity against a variety of Gram-positive and Gram-negative organisms and also inhibited β-lactamase produced by various bacteria. In the note we wish to report the fermentation, isolation and structure of PS-5.