The purpose of this study was to investigate children`s understanding of false beliefs by age, sex, and type of questions and development of cognitive perspective taking and examine its relation. The subjects were 72 children, 12 boys and 12 girls at 3, 4 and 5-year-olds. The data were collected by individual testing and analyzed by three-way ANOVA with repeated measures, two-way ANOVA, one-way ANOVA, paired T-test, Pearson`s Correlation and Multiple Regression. The major results were as follows. 1. Children`s understanding of false beliefs increased with age. And there were significant difference in performance according to the type of questions. In performance of question about others belief, significant difference were found among 3- year-olds, 4-year-olds, and 5-year-olds. While in performance of question about predicting other`s behavior, significant difference were found between 3-year-olds and 5-year-olds. The result suggest that the development of ability to represent other`s belief is prior to predict other`s behavior from false belief. Besides, gender did not affect the children`s understanding of false beliefs. 2. In children`s cognitive perspective taking (other-intented perspective taking, other-thought perspective taking) significant difference were found between 4-year-olds and 5-year-olds. And gender did not affect the children`s cognitive perspective taking. 3. The understanding of false beliefs and cognitive perspective taking showed significant positive correlation. That is, the children of high grades for cognitive perspective taking were better understanding of false beliefs. 4. Children`s age and other-thought perspective taking predicted children`s understanding of false beliefs. 41% of the variance of children`s understanding of false beliefs was explained by these two variables. But children`s sex and other-intented perspective taking hardly explained children`s understanding of false belief.