In Japan, as a measure to prevent puerperal infection, oral antimicrobial prophylaxis has been conducted after delivery in many maternity clinics. However, there are only a few reports on the evidence supporting the validity of antimicrobial prophylaxis following normal delivery. There is concern that unnecessary antimicrobial administration may be conducted in such clinics. In the present study, the puerperal females after normal delivery were placed on different treatments. A group of females received no oral antimicrobial administration. The remaining females were given cefteram pivoxil (CFTM-PI) in the two different doses. In this manner, we evaluated usefulness of antimicrobial prophylaxis. We compared three treatment groups with respect to the incidence of infection for the period until the first week after discharge, and obtained the following results: non-antimicrobial prophylaxis group (group A), 5.83%; antimicrobial prophylaxis group (group B), 1.77%; antimicrobial prophylaxis group (group C), 0%. In group B, the puerperal females were orally given CFTM-PI in a total daily dose of 300 mg, three times daily for three days. In group C, the puerperal females were orally given CFTM-PI in a total daily dose of 300 mg, three times daily for five days. The incidence of infection was the lowest in group C which was followed by group B and group A in this order and the significant intergroup difference was recognized (p=0.004). We also compared the total counts of bacteria, aerobes and anaerobes in lochia on the fifth day during the puerperal period with those on the first day in each treatment group. The decrease in bacterial count was the largest in group C, which was followed by group B and group A in this order. Compared with the total bacterial counts obtained on the first day, those obtained on the fifth day decreased significantly (p<0.001). The results of the present study showed usefulness of antimicrobial prophylaxis after normal delivery. As one of the factors, a significant decrease in the count of bacteria in lochia seems to contribute toward producing the satisfactory outcome.