Objective: The aim of study was to investigate the relationship between anthropometrical and physiological characteristics with performance of elite young boys in crawl and backstroke. Methods: This study was a descriptive research, 122 elite young boy swimmers (mean age 12-13 years; height 1.540±8.24m; weight 47.820±6.84kg), who participated in 2018 national championship 2018 in Shiraz and completed satisfaction letter. Results: There was a significant negative relationship between foot length (r=-0.400,P=0.028), leg power (length jump)(r=-0.477,P=0.008), static balance (r=-0.380,P=0.038) and dynamic balance (inferior) (r=-0.367,P=0.046) with 100m crawl (n=30) time. Whereas, there was a significant positive relationship between leg action and reaction velocity (r=0.438,P=0.015) with 100m crawl time. There was a significant negative relationship between head circumference (r = -0.507,P=0.019) with 400m crawl (n=21) time. Whereas, there was a significant positive relationship between leg power (length jump) (r=0.543,P=0.011) with 400m crawl time. There was a significant negative relationship between trunk circumference at nipple height (r=0.381,P=0.038), trunk circumference at hip (r=-0.523,P=0.003), forearm length (r=-0.412,P=0.024), hand length (r=-0.400,P=0.029), and tight length (r=-0.461, P=0.010) with 100m backstroke (n=30) time. There was a significant negative relationship between seated height (r=-0.399,P=0.039), hand length (r=-0.400,P=0.039), and tibia length (r=-0.415,P=0.032) with 200m backstroke (n=27) time. Whereas, there was a significant positive relationship between trunk circumference at hip (r=0.600,P=0.001), and leg power (high jump) (r=0.408,P=0.035) with 200m backstroke time. Conclusion: There was the relationship between anthropometrical and physiological characteristics with performance of elite young boys in crawl and backstroke. It´s recommended that coaches and swimmers pay attention to results of the study at the earliest stages of adolescence for getting more success in reaching the peak of athletic performance.