Background: Combination treatment with bevacizumab and paclitaxel has been approved for treating human epidermal growth factor receptor 2(HER2)-negative metastatic breast cancer(MBC) in Japan. Japan has no official economical guideline showing decision criteria for the approvals of new drugs. However, the National Institute for Health and Clinical Excellence(NICE) in UK hardly recommends the combinational use of bevacizumab for HER2-negative MBC, because of its poor cost-effectiveness.　Objective: The evaluation of the cost-effectiveness of additional bevacizumab as primary chemotherapy for HER2-negative MBC in accordance with the clinical practice guideline in JapanMethods: A Markov cohort simulation was used to follow the clinical course of typical patients with MBC. Transition probabilities were estimated from randomized clinical trials. Direct medical costs were assessed from the perspective of the Japanese health-care system. This study used quality-adjusted life year(QALY), and both costs and QALYs were discounted 3% annually. The time horizon was 10 years. Both a univariate and probabilistic sensitivity analyses were conducted. Results: The additional use of bevacizumab to paclitaxel required an additional cost of JPY 9.12 million(USD 114,000) for obtaining a gain of 0.26 QALYs, and the incremental cost effectiveness ratio was JPY 35 million(USD 437,000). Conclusion：By assuming of GBP 20,000-30,000(JPY 2.5-3.75 million and USD 31,000-46,900) to be an index value threshold by NICE, combination treatment with bevacizumab was found to be hardly cost-effective. Based on the fair and adequate distribution of medical resource, economical guidelines reflecting the Japanese health-care system are necessary. (Jpn J Pharmacoepidemiol 2013；18(1)：1-12)