The purpose of this study was to analyze the effects of the instruction of the standing long jump on children with autism and Down's syndrome by biomechanical methods. Five autistic children (autism group; age 11.0±1.0 yr) and 3 Down's syndrome children (down group; age 11.5±0.5yr) participated in this study. The subjects were instructed standing long jump by group education once per week for 4 weeks. The performance was analyzed by 2-D video system before and after instruction, and the length of jump, the phase time and the joint angle were evaluated. As a result, in the length of standing long jump, there were no differences significantly between autism group and down group, however, the values of both groups increased after instruction (p<0.01, p<0.05). The time from the initial static point to the landing point in autism group was significantly shorter than that in down group (p<0.05). After instruction, the time from the initial static point to the landing point was significantly increased in the both groups (p<0.01). And the ranges of motion of the shoulder joint in the both groups were significantly higher than those before the instruction (p<0.05). From these results, the pattern of standing jump was changed after instruction. Our study suggested the children with autism and Down's syndrome have potential to improve the standing long jump influenced by the group instruction.