In order to investigate the properties of cephalospornase, a strong antibiotic resistant strain(H 112) was isolated from Pseudomonas aeruginose. The extracted enzyme had the following characteristics. Optimum temperature was 45.deg.C and unstable over $55^{circ}C$, and optimum pH was 8.5. Cephalosporinase activity was not inhibited by metal ions such as $Mn^{++},;Cu^{++};Fe^{++},;Fe^{+++}$, and EDTA. But it was inhibited by some antibiotics such as carbenicillin, cefoxitin, cefotaxime, cefamandole, cefoperazone and SDS. The Vmax values of the enzyme were 100 at cephaloridine and 2.8 at cefoperazone, respectively. The molecular weight of cephalosporinase was estimated to be about $37.500{pm}3,000$ by high performance liquid chromatography and nitrocefin reaction.