摘要Background: Ethical problems in the nursing profession are mostly found in the undesirable ethical behavior (EBE) of nurses. If there is no concern about these problems, it may negatively affect the quality of nursing care, patients' safety, and trust in the nursing profession. In assessing nurses' EBE, it is important to develop an instrument that reflects the actual EBE of nurses. Objectives: To develop and evaluate the psychometric proper ties of the Ethical Behavior for Thai Nurses Scale (EBTNS). Methods: The construct definition, 5 sub-constructs, 43 items, and the hypothesized model were synthesized and generated from a comprehensive literature review and existing research instruments by using document analysis. The EBTNS was verified for content validity by 4 experts. Of the 43 items, 37 items were retained for psychometric testing. The construct validity was tested by using second-order confirmatory factor analysis (CFA). The EBTNS was tested on 1500 professional nurses working at tertiary, secondary, and primary hospitals in 6 regions (the central, northern, northeast, eastern, western, and southern) of Thailand. Proportional quota sampling was applied to recruit participants. Results: The hypothesized model fitted the empirical data. All 37 first-order indicators and 5 second-order sub-constructs showed significantly standardized factor loadings and effect sizes. The standardized factor loadings of 37 first-order indicators ranged from 0.58 to 0.89, and the construct reliabilities were moderate to substantial (R2 = 0.34–0.79). The 5 second-order sub-constructs displayed the standardized effect sizes, ranging from 0.81 to 0.96, and accounted for 65％–96％ of the total explained variance. In addition, the construct validity was supported by convergent validity and discriminant validity. It also satisfied Cronbach's alpha coefficients of 5 sub-constructs from 0.87 to 0.94, and a full scale was 0.97. Conclusions: The psychometric properties of the EBTNS are acceptable. This instrument has the potential to be used for evaluating and monitoring to prevent ethical problems of Thai nurses.