The properties of microbial L-alpha-glycerophosphate oxidase (GPO) isolated from a mutant strain of Aerococcus viridans DBM 1509 were estimated. The stability at different temperatures and pH were detected. At 4 degrees C the enzyme lost activity during 15 d, at 20 degrees C and 30 degrees C GPO activity decreased during 30 and 25 h, respectively. The highest stability was measured at - 20 degrees C and pH 9. At 4 degrees C the stability was enhanced by the addition of 0.1 M EDTA or by lyophilization in the presence of dextrin. These conditions allow the prolongation of the low stability of microbial GPO which limited its use, and give the opportunity to increase the stability of other enzymes