OBJECTIVE: Korea has implemented the new prescription drug policy in 2000, which separated the function of prescribing and dispensing drugs between doctors and pharmacists and purposed to improve the quality of drug use and remove the economic incentive from doctor's prescribing behavior. The aim of this study was to understand the adoption rates of new drugs in outpatient care after the new policy, and explore the effect of the policy on the adoption rates. METHODS: Four new prescription drugs frequently prescribed in ambulatory care were selected. From 1999–2002, the National Health Insurance (NHI) claims data for prescription drugs of selected clinics was used. The dependent variable was the adoption rate defined by the period from the enlisted date of the new drug on the NHI reimbursement list to the first prescribed date by each clinic. The explanatory variables were collected from the adopter, technology, and environment characteristics including policy change. The claims data was merged with telephone survey data. Cox's proportional hazard regression was performed to set and test the model in explaining the factors influencing on the adoption rate. RESULTS: The 1,792 observations were inputted into the model. The model showed that the new prescribing system made the adoption rate faster than before the change (HR=295.7, p<0.001) but the reimbursement restriction policy restricted the adoption rate of new drugs (hazard ratio (HR) = 0.03, p<0.001). The behavioral characteristics also influenced on the rate of adoption. Doctors who prescribe more number of drugs per claims and have higher proportion of drug costs per total medical costs were early adopters (hazard ratio 1.02, p<0.05). In addition, the innovative drugs and the drugs by multinational manufacturers were adopted earlier. CONCLUSIONS: The prescribing system change accelerated the new drugs to be adopted earlier, but the reimbursement restriction policy trade off this tendency.