The purpose of this study was to investigate children's and parent's perceptions of preschool children's serious fighting and rough-and-tumble play. Some research has combined serious fighting and rough-and-tumble play under the same category, namely, aggression. However, several studies have shown these two types of behavior have different characteristics and functions. In the present study, four questions will examine: (a) Do children and parents reach a high consensus in describing videotaped episodes as either serious fighting or rough-and-tumble play? (b) What criteria will be used frequently in describing children's aggressive play? (c) Comparing children and parent, which group will have higher agreement with expert in judgment for children's serious fighting and rough-and-tumble play? (d) Does the gender of children in the videotape influence parent's and children's judgment for serious fighting and rough-and-tumble play? Thiryt-five parents and 33 young children were selected for this study. A videotape of 8 play episodes were run for all subjects. The play ground behavior of preschool children at a day care center were shown. Parents and children were asked to write down or answer whether the incident is serious fighting or rough-and-tumble play and the reason for their judgment. Results indicated: (1) There were significant difference between two groups on five episodes. (2) The most frequently used criterion was inference action or intent. It was followed by physical actions. (3) The parent group reached higher level of agreement with expert. (4) Gender (boy-boy interaction and boy-girl interaction) affected parents' and children's perception of serious fighting and tough-and-tumble play.