In this study, the readability of the texts in the third and the sixth grade science textbooks developed under the 2007 revised science curriculum were analyzed in terms of word and sentence units. In the word unit analyses, the levels of the words in the texts were classified into four categories, 1st to 4th levels. In the sentence unit analyses, the sentences in the texts were classified either a simple sentence or compound/complex sentences, and the average length of the sentences was also calculated. The results indicated that more than 90 percents of the words in the 2007 revised science textbooks were classified as the 1st to the 3rd levels. However, both the kinds and the frequencies of the words in the 2007 revised science textbooks were increased in comparison of those in the 7th science textbooks. In particular, it was found that the increasement in the 3rd grade science textbook was noticeable. The ratio of the compound/complex sentences in the 2007 revised science textbooks were increased in comparison of those in the 7th science textbooks. The average length of the sentences in the 2007 revised science textbooks was also increased.