Pharmacist-managed Anticoagulation Service(ACS) was estabilished and the effectiveness of warfarin monitoring by ACS in maintaining therapeutic INR was evaluated. The primary goal of ACS is to maximize the control of therapy, to maintain therapeutic INR and to decrease morbidity and hospitalization caused by inadequate dosage regimen. Clinical pharmacists performed chartreview, laboratory interpretation, recommendations for warfarin dosage adjustments, physician and patient education, and coordination of follow-up in ACS. Patients receiving warfarin sodium were evaluated via retrospective chart review. Sixty-two patients were referred to ACS by primary physicians were compared with 117 patients in the physician-amtrolled group. The ACS patients maintained $88.6\%$ in the therapeutic range for anticoagulant therapy and the control group maintained $63.7\%$, where the difference was statistically significant.(P<0.001) The ACS improved warfarin dose determination, PT stability, patient compliance and provided improved therapy compared with the control group. ACS offers safe and efficient anticoagulant therapy in the ambulatory setting.