The major focus of this investigation was aggressive behavior and aggressive fantasies in preschool children between the ages of three and five years. Time samples of aggressive behavior during free play were compared with the fantasy expression of aggression in a standardized doll play situation. 　　The expression of aggression both overtly and in fantasy increased with age. Boys showed more overt aggressive behavior than girls. However, there were no sex differences in the doll play situation. All of the children showed a larger number of aggressive responses in thier free play than in their imaginary doll play. The correlation between the two situations was approximately zero (rank correlation coefficient: 0.09). One factor contributing to this difference may have been the verbal responses required by the situation which were too difficult for the three and four year old children. Another possibility is that the children simply did not find the doll play situation as frustrating as their peer interactions, these results suggest that the expression of aggression in children is situation oriented. In child-child social interaction, a youngster's aggressive impulses are more likely to be stimulated than in a doll play situation.