Background: The present study investigated sports knowledge, attitude, and practice in adolescent athletes in Tehran, Iran. Methods: Data were collected using the Sports Nutritional Knowledge, Attitudes, and Behaviors questionnaire (SNKABQ), completed by 174 high school students in Tehran aged 15 - 18 years (85 females and 89 males). The original version of SNKABQ was designed in English and, in this study, was translated into Persian and adapted to the Iranian nutritional culture. The SNKABQ has devoted five sections: Demographic information, eating and drinking habits, attitudes toward nutrition, knowledge of nutrition, and resource nutritional information. Data analysis was performed using descriptive statistics, the Mann-Whitney U test, the Kruskal-Wallis test, and Pearson's correlation coefficient. Results: The mean total score was 59%, while the mean scores of 66%, 63.4%, and 48.71% were recorded for sports nutrition knowledge, attitude, and practice, respectively. No significant differences were observed in the sports nutrition knowledge and attitude between the male and female students (P ≥ 0.05). However, the male students selected more appropriate feeding methods than the females (P = 0.009). In addition, school area and sports type affected the level of sports nutrition knowledge, attitude, and selection of proper nutritional behaviors. Conclusions: According to the results, the adolescent athletes aged 15 - 18 years in Tehran do not have sufficient sports nutrition knowledge, attitude, and practice, or if they have some correct expertise in some parts, they usually cannot apply their information. Therefore, it is suggested that effective measures be taken to increase the nutritional knowledge of adolescent athletes to maintain their health, ensure their growth, and facilitate their athletic progress.