The purpose of the present experiments was to investigate the development of awareness of referential ambiguities in messages. Subjects were 149 preschool children (3-, 4-, and 5-year-olds) and 45 adults. Each subject was asked to detect message ambiguities by pointing to a question mark in the alternatives and give reasons for such responses. In addition, the subject was required to produce an adequate message about the experimenter's chosen drawing in the alternatives. Results suggested the following several levels of awareness of referential ambiguities. Level 1: Subjects could not recognize ambiguities and specified referents “egocentrically.” Level 2: Subjects could detect ambiguities by behavioral responses, but could not give adequate reasons for such responses. Level 3: Subjects could detect ambiguities and give adequate reasons for the detections. In addition, results showed that it was more difficult to produce adequate messages than to recognize the ambigaities in messages received. These problems of level distinction were discussed in terms of Flavell's meta-cognition theory and Piaget's “grasp of consciousness” theory.