In EFL countries where English is rarely practiced outside the classroom, textbooks have become the major input source for learners. Particularly in Vietnam, multiple textbook series are available simultaneously for the same grade. Thus, it is important to examine if their vocabulary is appropriate and of similar difficulty. This study aims to investigate and compare the lexical demands, sophistication, diversity, and lengths of reading passages in the eight latest series for Vietnamese 10th graders with 53,360 tokens in total. The results revealed that the most frequent 1,000, 2,000-3,000, and roughly 4,000-word families in the BNC/COCA wordlist, plus proper nouns, marginal words, transparent compounds, and acronyms, were respectively needed for 85%, 95%, and 98% coverage. Additionally, pairwise comparisons uncovered that the passages differ significantly in length yet insignificantly in lexical sophistication and diversity. Therefore, the series appear to be well-suited to co-implementation and facilitative to vocabulary development despite not being optimized for independent learning. The study still calls for simplifying the eight textbook series to promote meaning-focused output. Finally, implications for exploiting and revising these textbook series are discussed.