The author examined whether children's understanding of lies exhibits developmental trends in the elementary school years. Four story contexts were presented to 51 first-grade students, 44 fourth-grade students, and 58 adults. These stories represented combinations of a protagonist's intention (truthful or deceptive) and the truth of the protagonist's message (true or false). The results showed that adults judged whether these messages were lies by considering the protagonist's intentions. By contrast, approximately 30% of first-grade students and some fourth-grade students did not consider intentions in making judgments, although they appropriately predicted the outcomes of the messages. These results suggest that children in the early elementary school years have a conception of lies different from that of adults, and their conception of lies becomes more sophisticated after middle childhood.