Given Vietnam's economic growth and globalization, English education has become increasingly prominent, as evidenced by government policies and a heightened emphasis on English in the national curriculum and textbooks. In light of this, the present study examines the evolution of English language education in Vietnam by analyzing the revisions of upper secondary English textbooks based on the 2012 and 2018 curricula. The research seeks to comprehend the changes in thematic contents and readability levels employed in these textbooks. To achieve this, the study analyzes the themes of individual reading passages and the readability level, including fundamental text characteristics, to gain insights into the evolving landscape of English education in Vietnam. The findings reveal significant shifts in the thematic focus, and content distribution between the two editions. Although both curricula share similar topic categories and approaches to subtopics for the reading passages, the 2018 revised edition places a distinct emphasis on the "Our Lives" theme in terms of content distribution. The analysis also identifies discrepancies between the intended curriculum goals and the actual text characteristics of the reading passages, highlighting the need for a more rig...