Previous studies suggest that one characteristic of friendship should be similarity in terms of attributions, attitudes, and behavioral tendencies. Using an experimental approach, the present study investigated whether preschool children judge that similarity in physical appearance or behavioral tendencies affects friendship selection. Experiment 1, which used human-like figures as stimuli, revealed that both 4- and 5-year-olds (n = 32 and n = 30, respectively) judged that similar physical appearance affects friendship selection. We conducted a second experiment to test whether children were making judgments according to friendship selection, and not merely physical similarity; thus, in Experiment 2, we used nonhuman figures as stimuli, and found that 5-year-old children (n = 31) judged that similar physical appearance would affect friendship selection, whereas 4-year-old children (n = 31) showed no significant responses to any stimuli; this might be related to the development of the ability to make mental attributions to inanimate figures. The present findings suggest that young children regard similar physical appearance as an important factor for friendship selection. At least at the age of five, similarity might be an antecedent to friendship.