This study examined the reading passages of the National Assessment of Educational Achievement (NAEA) and middle school English textbooks in terms of their readability and lexical difficulty. The readability was measured by using Flesch-Kincaid Grade Level Index, while their lexical difficulty was measured in terms of STTR (standardized type-token ratio), frequency of tokens per type, and vocabulary frequency levels by using VocabProfile and Oxford WordSmith Tools 7.0. The results showed that there was a gap between the readability of the English textbooks and that of the NAEA conducted from 2012 to 2014, while the readability between the English textbooks and that of the 2015 NAEA reached a comparable level. However, the textbooks from one publisher showed substantively lower readability than those from the other publishers and the NAEA. Secondly, regarding vocabulary frequency levels, the words in 1K and 2K accounted for more than 90% of the textbooks and the NAEA, while the NAEA had a higher STTR and lower frequency of tokens per type than the textbooks. It suggests that the NAEA employed more various words with less repetition than the textbooks. Pedagogical implications are discussed.