The BOX-O3 is a new, alternative apparatus that uses ozone for the disinfection of biomedical waste. This study evaluated the ability of the apparatus to disinfect contaminated medical and laboratory waste that included a variety of bacterial strains. Microbiological measurement was done on laboratory waste contaminated with a variety of bacterial strains, medical waste alone, and medical waste contaminated with Bacillus subtilis collected from the infectious disease ward of Kyushu-university hospital. The strains tested for were Bacillus subtilis, Pseudornonas aeruginosa, Staphylococcus aureus, Enterococcus faeciurn, and Candida albicans. A 100mL (5 test tubes containing 20 mL each) bacterial suspension consisting of 108 to 109 colony forming units (CFU)/mL was added to waste in a container. The mean bacterial load of the waste was measured immediately after shredding and ozone treatment. Three samples were recovered from three different places at random in the bulk ground. The samples were diluted to 1:10 and 1:100, then cultured at 37°C for 48 hr in a blood agar medium. For the measurement of primary bacterial load, shredding alone was done without the boost additive (hydrogen peroxide and acetic acid) and ozone treatment. All assays were done in triplicate. In the laboratory waste contaminated with a variety of bacterial strains, all bacterial populations were decreased by at least 4 log10 immediately after ozone treatment. The primary mean bacterial load of the untreated medical waste alone was 3.8log10 CFU/g, and only normal flora was observed. The primary mean bacterial load of the untreated medical waste contaminated with Bacillus subtilis was lower than that of the untreated laboratory waste contaminated with Bacillus subtilis. In the medical waste contaminated with or without Bacillus subtilis, no bacterial populations were detectable immediately after ozone treatment. The BOX-O3 safely and efficiently treated infectious medical waste collected from hospital ward, indicating that the BOX-O3 is an effective alternative technology for the treatment of infectious waste and for controlling hospital infection.