Background. Of children and teenagers aged 6–19, 16% (almost 9 million) were obese (i.e. Body Mass Index at or above the 95 ^th percentile for children of the same age and sex) and this number has continued to increase. Increased understanding of proper nutrition and the need for physical activity among adolescents will likely prevent health problems associated with overweight and obesity, and improve quality of life into adulthood. In particular, when considering determinants of obesity responsive to change, a focus on modifiable, prevalent, and relevant behaviors among adolescents should be taken. Purpose. The purpose of this study was to examine the extent to which constructs of the Theory of Planned Behavior (TPB) (behavioral intent, attitudes, social norms, and perceived behavioral control) predicted four behaviors linked to childhood obesity in middle school children: daily physical activity, sedentary behaviors, fruit and vegetable intake, and water versus sweetened beverages consumption. In addition, a valid and reliable instrument which adequately reified the constructs of the TPB in relation to the aforementioned behaviors was developed. Methods. A cross-sectional design was implemented to obtain a convenience sample of 318 middle school students. Prior to the administration of the instrument to the entire student population, factor analysis and reliability estimates were conducted with a sub-group of students. The 129-item instrument was administered during health, physical education, and art classes. Multiple regression and structural equation modeling were used to establish the predictors for each behavior. Results. Almost 25% of the students were considered overweight or obese. Students did not meet the recommended five servings of fruit and vegetables per day (M = 3.67); participated in more than the 1-2 hours recommended screen time (M = 187.42 minutes); and had an increased risk of obesity with their sweetened beverage consumption (M = 1.59 glasses) per day. The mean behavioral intention scores for the behaviors were as follows: screen time behaviors (M = 12.31, SD = 5.42); physical activity (M = 12.84, SD = 7.18); fruit and vegetable consumption (M = 12.18, SD = 5.74); sweetened beverages versus water consumption (M = 12.42, SD = 6.07) – denoting a moderate intent to participate in the behavior. Regression results showed that behavioral intention was predictive for screen time among overweight and obese students, participation in physical activity among all students, consumption of fruits and vegetables among overweight and obese students, and consumption of water versus sweetened beverages in normal weight students (p < 0.05). The most predictive constructs of the Theory of Planned Behavior were subjective norms and perceived behavioral control – accounting for up to 11.4% of variance in the behaviors. Conclusion. Behavioral intention was linked to the four behaviors suggested for obesity prevention in adolescents. Differences among those students who were considered normal weight and overweight/obese existed, and should be considered when designing future programs. The Theory of Planned Behavior presented a beneficial framework for improving behavioral intention among adolescents, with hopes to progress toward positive behavior change in nutrition and physical activity behaviors.