In their play, children often use some objects to designate and replace others. We call such use of objects "symbolic use", the objects "signifiers" and the designated objects "signified". The purpose of the present study is to examine: (1) the role of play activities in symbolic use, (2) the developmental change of symbolic use. 64 nursery school children, aged from 3 to 6, took part in these three experiments. <Experiment I (outside of play 1)> 8 objects are presented one by one and each S is asked whether the object (signifier) can be used or not as a certain suggested object (signified). <Experiment II (outside of play 2)> Each S is told a fairy tale and presented some figures (signifier) representing, in varying degrees of similarity, the characters (signified) in the story. The S is then asked to choose which figure he sees as representing the character in the story. <Experiment III (inside of play)> The same objects, as in the Experiment I, are presented in the role-taking-play whith a certain suggested theme. Each S is observed to see if he can actually use the object as a certain suggested object as in the Experiment I. Comparing the results in the Experiment I and III, inside of Play (Experiment III), We may infer that "symbolic use" is easier than outside of play (Experiment I). "Symbolic use" can be achieved inside of play so long as the objects can support the same activities as the signified objects, regardless of the dissimilarity of the object to the "signified". Outside of play, however, "symbolicuse" is more difficult, especially with objects which are distinctly different from that "signified". These results suggest that actual symbolic use may facilitate symbolic function in children. Concerning the development of symbolic use, cases inside of play are more observed in the older age group than in the younger, and cases outside of play are more often recorded in the younger than in the older age group. In the former type of "symbolic use", the object and its "signified" are joined by play activities, regardless of the difference between them; therefore, children in the older age group who have the former experience of play activities and play themes make this type of "Symbolic use", more readily than the younger. On the other hand, in the latter type of "symbolic use," the object and its "signfied" are joined in their similarities. Then the older children who can discriminate strictly the difference between the two make this type less readily than the younger. In conclusion, we may infer that among these two types of "symbolic use", "symbolic use" inSide of play might be the main road of development of symbolic function in children, leading to the level of "sign" wherethe "signifier" sharply differs from its "signified".