Vancomycin hydrochloride (VCM) is widely used for treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. However, this drug can cause sever adverse reactions, such as red neck syndrome, nephrotoxicity and ototoxicity. Thus, therapeutic drug monitoring (TDM) was bringing into effect for well effectiveness and to prevent side effects. In Kanto Medical Center NTT EC, TDM of VCM has been brought into effect since 1994. The date were accumulated from 200 patients. In this study, the retrospective research was carried out based on 117 cases selected from the above accumulated data, and then several factors such as VCM inducing side effect, a therapeutic effect, and the forecast of pharmacokinetic parameter using laboratory data were examined. Consequently, the high blood concentration trough level, the high value after 1 to 2 hours infusion, and the extension of t1/2 were brought forward as a nephrotoxicity causing factor, and more over each laboratory data (BUN, Cr, GOT, GPT, γ-GTP, T-BiL, ALP, LDH) was high before infusion of VCM in patients with renal dysfunction. High value T-Bil and lower value TP were brought forward in patients with hepatic dyfunction, and high eosinophils and high blood concentration were brought forward after 1 or 2 hours infusion. In relation to side effects, it was found that the outbreak rate of side effects is high in patients with a complication of hypertension or diabetes. The administration term was considered as a factor which influences the therapeutic effects. The unchanged effect was 10.9±7.9 days, the improved effect was 14.6±9.3 days, the remarkably improved effect was 17.7±14.1 days. As the administration term gets longer, the improvement rate was recognized to be an upward tendency. The difference in significant effects was recognized between unchanged and remarkably unchanged (p<0.05) effects. As the forecast of pharmacokinetic parameter using the laboratory data, VCMt_1/2 showed a significant correlation between Cr and T-BiL, and it was VCMt_1/2=8.56Cr+2.169T-Bil+7.1. This result shows that VCMt_1/2 can be estimated.