The purpose of this study is to devise a new method for examining the readabilities of textbooks and to compare the readabilities of elementary school science textbooks. Third and sixth grade science textbooks were compared in terms of word, sentence, and paragraph in this study. In the word analyses, criterion suggested by Kim (2003) who classified about 238,000 words into seven categories according to their educational importances was adopted. In this study, the words from 3rd and 6th grade science textbooks were classified into four categories, and then the kinds and frequencies of words in each category were investigated. In the sentence analyses, sentences were classified either a simple sentence or a compound/complex sentence, and the ratios of each type were calculated. The average number of words in a sentence was also calculated in the sentence analyses. The ratios of conjunctions and demonstratives were examined in the paragraph analyses. The results indicated that both the kinds and frequencies of words in 3rd grade science textbook were smaller than those of 6th grade one. However, both science textbooks were similar in the distributions of words across the four categories. The ratio of simple sentences in 3rd grade science textbook was higher than that of 6th grade one, and the length of a sentence in 3rd grade science textbook was also shorter than that of 6th grade one. Both the ratios of conjunctions and demonstratives in 3rd grade science textbook were lower than those of 6th grade one.