Three kinds of tight skirts, slim type, straight type, and semi-tight type were investigated to obtain necessary information about the size of the back slit. Fourteen college students put on these experimental clothes and walked on the flat floor, going up and down the stairs. The dimensions of the back slit were measured by width and length. The stride length was taken from the record of footprints of walking. The correlation between the body measurement, stride length and the size of the back slit was studied. As a result of this experiment, the findings are as follows: 1. The size of the back slits differed from each skirt type at the level of p<0.001. In the case of walking on the floor, the average dimension of the back slit was 14.0 cm long 5.0 cm wide for the slim type,9.5 cm long 2.8 cm wide for the straight type and 2.1 cm long 0.5 cm wide for the semi-tight type. 2. In the case of walking on the stairways, the average dimension of the back slit was 16.0 cm long 5.8 cm wide for the slim type, 12.4 cm long 3.9 cm wide for the straight type and 3.1 cm long 1.1 cm wide for the semi-tight type. 3. The correlation between the height (stature, waist height, knee height) and the size of back slit was 0.3 to 0.6. The correlation between the girth (waist, hip) and the size of back slit was 0.3 to -0.5. 4. The correlation between the stride length and the size of back slit was 0.76 for the slim skirt, 0.56 for the straight skirt, 0.28 for the semitight skirt.