The gay affirmative practice (GAP) scale is an effective tool for evaluating the beliefs and behaviors of health care professionals toward gay and lesbian clients. This study aimed to examine the reliability and validity of the GAP scale among Chinese nurses. A quantitative cross-sectional study was conducted to evaluate the Chinese version of the GAP (C-GAP) scale after translation and cross-cultural adaptation and to examine its psychometric characteristics. The reliability and validity of the C-GAP scale were determined by item analysis, factor analysis, internal consistency, test-retest reliability, and discriminant construct validity. The GAP scale was translated and adapted specifically for China. A total of 1440 participants completed the C-GAP scale, sociodemographic questionnaire, and Marlowe-Crowne social desirability scale. The C-GAP scale exhibited a Cronbach α of 0.95, with a high test-retest reliability coefficient of 0.92. Exploratory factor analysis identified 2 factors that accounted for 59.91% of the total variance. The results of the confirmatory factor analysis were as follows: χ2/df = 1.09, goodness-of-fit index = 0.98, adjusted goodness-of-fit index = 0.97, root mean square error of approximation = 0.01, Tucker-Lewis index = 1.00, comparative fit index = 1.00, incremental fit index = 1.00, parsimony goodness-of-fit index = 0.85, and parsimony normed fit index = 0.91. These findings confirm that all goodness-of-fit indices were satisfactory. The C-GAP scale can be an effective tool for health care professionals and managers and for education and research; it can also identify the beliefs and behaviors of health care professionals toward gay and lesbian clients, facilitating cultural competence development and enhancing care quality awareness and skills. The C-GAP scale demonstrates reliability and validity; however, because the sample consisted only of nurses, the findings may not be generalizable to other professional groups, such as counselors and therapists. Therefore, the occupational focus of the sample limited the broader applicability of the results. The C-GAP scale is a reliable and valid tool suitable for assessing the practice attitudes and behaviors of Chinese nurses toward gay and lesbian clients.