In this study, the effects of the authority level and the number of anomalous data on students' cognitive conflict and conceptual change in studying density were investigated. The subjects were 119 eighth graders in a co-ed middle school. A preconception test, a test of response to anomalous data, and a conception test were administered. Four types of anomalous data varying the authority level (high/low) and the number (one/two) were presented. The results indicated that anomalous data presented at high authority level significantly induced more cognitive conflict than that presented at low authority level. However, no significant difference in the degree of cognitive conflict was found between the number levels of anomalous data. The ANOVA. results indicated that there were no significant differences in the conception test scores due to the characteristics of anomalous data