OBJECTIVES: Adoption of new drug in medical care, a highly-regulated industry, is and essential in terms of access to new treatment option and raise on health care expenditure. This study, using Cox2 as example, is to examine the diffusion of new drug among hospitals of different characteristics. METHODS: The data were drawn from systematic random sample of NHI claim data in 1997 to 2001. We applied the Bass diffusion model to analyze the monthly number of each hospital's outpatient clinic visits with COX2. Bass diffusion model based on the initial time of purchase of product to explains the behavior of the diffusion of the product in the market: length to reach maximum monthly volume, maximum monthly volume, growth rate. RESULTS: The estimates of Bass diffusion model shows that the monthly numbers of outpatient clinic visits with COX2 prescription reached the stable maximum in the 92th month, 41 months after the introduction of COX2 on April of 2001. The length of growth period for reaching maximum volume varied with different accreditation level of hospital: academic medical center 38 months, metropolitan hospitals 43 months, local community hospitals 40 months, and physician clinics 51 months. The average of maximum volume for academic center was 76.17 outpatient visits, metropolitan hospitals 87.25 visits, local community hospitals 62.65 visits, and physician clinics 34.38 visits. Physician clinics has the fast growth rate (q=0.1278), in contrast to the slowest of local community hospitals (q=0.1159), CONCLUSION: Hospitals of different level vary in terms of adopting new drugs. Academic medical centers play the role of innovators.