In bovine mastitis, antimicrobial treatment is often initiated before the causative organism is identified a problem in the prudent use of antimicrobials. In this study, we aimed to reduce the total amount of antimicrobials used in mastitis treatment by administering glycyrrhizin, an anti-inflammatory drug, instead of antimicrobials at the onset of clinical mastitis without systemic symptoms, followed by symptom-based antimicrobial selection therapy (ST), to examine the effect of this treatment strategy on treatment outcomes and antimicrobial use. Comparisons between cases that received antimicrobial treatment starting from the day of diagnosis (blanket antibiotic therapy [BT] group: 33 cases) and cases that received ST starting from the day after the diagnosis (ST group: 57 cases) revealed no difference in the cure rate, milk withholding period, or recurrence rate. However, the ST group had a significantly lower amount of antimicrobials than the BT group. Additionally, a single administration of glycyrrhizin before ST significantly relieved the udder symptoms and reduced the antimicrobial amount when compared with cases without glycyrrhizin administration. Thus, a single administration of glycyrrhizin followed by ST can reduce the total antimicrobial use.