The article examines the effectiveness of using crossfit to improve the physical fitness of boxers. Relevance. The analysis of domestic and foreign sources shows that the issue of improving the physical qualities of boxers with the help of nontraditional means for boxing, taken from other sports, is not sufficiently studied. Problem, goal, tasks. The purpose of the study is to study the effectiveness of using crossfit to improve the physical fitness of boxers. Research objectives: to select and put into practice a crossfit complex to improve the physical fitness of boxers; to conduct a comparative analysis of the effectiveness of the development of physical qualities in boxers aged 15-16 years. Research materials and methods. The study involved 18 athletes aged 15-16 years, who were divided into two groups - experimental (8 people) and control (10 people). Boxers from the experimental group were engaged in crossfit twice a week at the end of the main part of the training session. The main method of research was pedagogical testing (the method of control tests). Results and discussion. As a result, it is shown that the inclusion of crossfit complexes in the training process of boxers aged 15-16 years had a positive effect on general and special physical fitness. Flexibility improved by 46 %, strength endurance improved by 45 and 35 %, speedstrength abilities - by 8 %, coordination - by 7 %, speed - by 5 %, in the test “number of hits on the bag in 3 minutes” the result improved by 8 %, in the tests “number of hits on the bag for 8 seconds” and “air strikes for 5 seconds” - by 10 %. Conclusions and conclusion. As a result, the positive effect of crossfit on the general and special physical fitness of boxers is shown. During the study period, the greatest change in the results occurred in tests requiring the manifestation of strength endurance, both in the experimental and control groups.