This paper aims to analyze English vocabulary in the latest secondary school textbooks of South and North Korea synchronically, using corpus linguistics. To perform the study, six English textbooks of North Korea published between 2001 and 2008 have been constructed as corpora. All the textbooks for secondary school in North Korea, and those that correspond to the same grade levels in South Korea were compared and analyzed. The vocabulary sizes of both categories are similar, but the word variations in South Korean textbooks are twice as much as those in North Korean textbooks. That means the vocabulary in the textbooks of South Korea are more diverse than those of North Korea. To compare the differences in vocabulary levels, the two corpora were analyzed with corpus-based analysis programs such as 2015 KBEWL and GSL-AWL. The results show that student defectors from North Korea will likely have difficulties learning some of the English vocabulary. Thus, it is necessary to develop extra vocabulary teaching programs and materials to help them adapt to English learning in South Korea