Using a simplified version of the Heider, F. & Simmel, M. (1944) animation, I examined the size effects of the two components appearing in the frame sequence. When the small circle moved ahead (small-large condition), 45 observers (54%) regarded the sequence as the chasing and 22 (27%) regarded it as the following. Contrastively, when the large circle moved ahead (large-small condition), 28 (34%) regarded it as the chasing and 39 (47%) as the following. In the second experiment in which the size of the two components was equalized, the observers responded similarly to the large-small condition of the first experiment, i. e., 39 observers (37%) regarded the sequence as the chasing and 49 (47%) as the following. Furthermore, in the second experiment a new sequence was introduced, where the first figure (the moving ahead figure) was caught up with by the second one. Under the condition, 51 observers (48%) regarded the sequence as chasing and 35 (33%) as the following. Thus the size change effects between the two component figure we clarified by the present experiments.