The popularity of using textbooks in second language programs in universities around the world continues to grow. Textbooks support teachers in their teaching by providing accessible materials and clear instruction. In addition, learners are guided by familiar lesson frameworks (e.g., beginning, middle, end) to guide their independent study (Swales, 1980). However, textbooks present many challenges. Learners' difficulties include the range in lexical knowledge they must possess (Nation, 2006) and the different lexical and grammatical features that are found in written textbook registers (Biber et al., 1998). This study investigates and outlines the vocabulary load of two English for Academic Purpose textbooks, using the British National Corpus and Corpus of Contemporary American English (BNC/COCA) 25,000 (Nation, 2012) and JACET8000 (JACET, 2016) word lists. The results show that for each textbook, more lexical demands are needed for second language learners in the JACET8000 compared with the BNC/COCA 25,000 lists. Understanding the content in textbooks will inform of the vocabulary-level requirements needed when taught in tertiary-level programs. Using a general and a Japanese-specific word list to identify possible pedagogical priorities can help to determine textbook priorities for teachers that can be applied to teaching in the Japanese classroom.