Purpose: This research aimed at the investigation of the readability level of 100 prominent authored fiction books for B, C, and D age groups, selected by Children's Book Council of Iran as an official institute for labeling and assigning level of children’s books in Iran.

Methodology: Evaluative research method was used for the implementation of this research. Research population consisted of 100 authored books, selected as “prominent” by the Council. Flesch/Dayani and Gunning/Dayani formulas were used as evaluative tools.

Findings: Results indicated that on the basis of scores extracted from Flesch/Dayani formula, 54/76 percent of the books correctly labeled by the Council as B, C and D. Again, Results showed that on the basis of Gunning/Dayani formula, 45/24 percent of the books correctly labeled by Council as B, C and D and 44/76 percent of the books have not been labeled correctly.

Originality/Value: We tried in this research to evaluate the act of labeling books, implemented by “Children’s Book Council” and the result of such an evaluation was some corrections in the formulas