High agility performance is important for football players and the acquirement of this skill has been discussed recently. The purpose of this study was to analyze the agility test and the motion of side-step cutting by biomechanical method. Twenty college-football players (mean ± SD age = 20.6 ± 1.4yrs; height = 174.0 ± 4.2cm; weight = 78.4 ± 12.0kg) were participated in this study. Subjects performed 40 yard straight dash and pro-agility test and assigned to three groups: group A; QB, WR, DB, group B; LB, RB, group C; OL, DL. For the biomechanical analysis of side-step cutting, three subjects with different levels of agility performed 5 yard dash in a straight line and change of direction. The angle of change of direction was 90 degree and 135 degree to the right. The motion of side-step cutting was monitored by two high speed digital video cameras and analyzed by a 3-D analysis system (DKH system, Japan). The total time, the contact time of left sole and the angle of left lower leg to the ground during the change of direction were analyzed. Correlation analysis showed relatively high validity between 40 yard straight dash and pro-agility tests (r = 0.715). The values of 40 yard straight dash and pro-agility test in groups A and B were significantly higher than in group C (p < 0.05). From the biomechanical analysis, the players with high scored pro-agility test showed the contact time was short and the angle of lower leg was small in both 90 degree and 135 degree. By player position, high agility performance was observed in QB, WR, DB. The players with high agility can perform side-step cutting with small angle of lower leg to the ground within a short span of time. From this result, minimizing the angle of ankle joint may produce larger horizontal power for change of direction. This study suggested the angle of lower leg to the ground is important for side-step cutting. The above is valuable information for coaches and athletes involved in improving the skill of agility.