abstract: Two studies were conducted to test a model to predict healthy lifestyle behaviors, physical activity, and body mass index (BMI) in Taiwanese adolescents by assessing their physical activity and nutrition knowledge, healthy lifestyle beliefs, and perceived difficulty in performing healthy lifestyle behaviors. The study drew upon cognitive behavioral theory to develop this study. The pilot study aimed to test and evaluate psychometric properties of eight Chinese-version scales. The total sample for the pilot study included 186 participants from two middle schools in Taiwan. The mean age was 13.19 for boys and 13.79 for girls. Most scales including Beck Youth Inventory self-concept, Beck Youth Inventory depression, Beck Youth Inventory anxiety, healthy lifestyle beliefs, perceived difficulty, and healthy lifestyle behaviors scales Cronbach alpha were above .90. The Cronbach alpha for the nutrition knowledge and the activity knowledge scale were .86 and .70, respectively. For the primary study, descriptive statistics were used to describe sample characteristics, and path analysis was used to test a model predicting BMI in Taiwanese adolescents. The total sample included 453 participants from two middle schools in Taiwan. The mean age of sample was 13.42 years; 47.5% (n = 215) were males. The mean BMI was 21.83 for boys and 19.84 for girls. The BMI for both boys and girls was within normal range. For path analysis, the chi-square was 426.82 (df = 22, p < .01). The CFI of .62 and the RMSEA of .20 suggested that the model had less than an adequate fit (Hu & Bentler, 1999). For alternative model, dropping the variable of gender from the model, the results indicated that it in fact was an adequate fit to the data (chi-square (23, 453) =33.75, p> .05; CFI= .98; RMSEA= .03). As expected, the results suggested that adolescents who reported higher healthy lifestyle beliefs had more healthy lifestyle behaviors. Furthermore, adolescents who perceived more difficulty in performing healthy lifestyle behaviors engaged in fewer healthy lifestyle behaviors and less physical activity. The findings suggested that adolescents' higher healthy lifestyle beliefs were positively associated with their healthy lifestyle behaviors. / Dissertation/Thesis / Ph.D. Nursing and Healthcare Innovation 2012