The use of corpus-based findings in order to inform L2 teaching materials have been emphasized by many researchers owing to the fact that the studies of authentic texts have revealed some inconsistencies between the use of grammatical structures in corpora, and those found in language textbooks that are based purely on hunch. Therefore, by comparing a textbook corpus with the British National Corpus, this study attempts to shed light on the extent in which modal auxiliary verbs presented in the Malaysian prescribed textbooks are identical with those used by native speakers. The findings showed that there are discrepancies between English language textbooks and real language use. Findings from this study contribute to the improvement of pedagogical practices in the teaching of the modal system and provide a sense of familiarity with textbooks' content thus assisting educators in identifying the particular strengths and weaknesses in textbooks already in use.