The Principles on Drug Reimbursement Price Approval(PDRPA) is the basis for pricing new pharmaceuticals for NHI reimbursement in Taiwan. PDRPA describes the scope of comparative treatments and defines the 3 categories of new drug as: 1 (breakthrough); 2A (moderate improvement); and 2B (similar) based on the comparative effectiveness of new drug to the current therapies, which links to the decision of pricing method used. The selection of comparator is crucial in technology assessment and has profound influence on the pricing decision. Hereby we explicitly describe the selection rules and roles of comparator(s). To sort out the rationale of comparator selection, the following 8 features of a comparator are considered: 1) indication(s) approved by department of health Taiwan; 2) associated reimbursement guidance; 3) ATC (Anatomical Therapeutic Chemical) classification; 4) clinical guidance of using the comparator on treating target disease by new drug; 5) comparative evidence such as head-to-head trial or indirect comparison; 6) NHI reimburse price; 7) prices of comparator in the 10 reference countries; and 8) recent utilization in NHI. Clinical relevant and appropriateness are the priority of comparator(s) selection. To be qualified as class 1 or 2A new drug, the currently best therapy should be used as comparator. Then one of the 6 pricing methods will be chosen to decide the reimbursement price of the new drug, with or without reimbursement guidance on using the new drug; and/or the decision to initiate price-volume agreement or (financial) risk sharing negotiation with the pharmaceutical company. Five possible roles of the comparator(s) would play in the assessment: 1) to justify the comparative effectiveness to the new drug; 2) to calculate the price of new drug; 3) to evaluate the net budget impact; 4) as reference setting for reimbursement guidance; and 5) be used in pharmacoeconomic study.