[eng] Based on the studies of previous scholars on the special importance of equipping English textbooks with cultural content, this study aims to clarify the integration of cultural contents in the old and the new English textbooks for Vietnamese students at upper secondary school level and at the same time, it aims to detect any changes in cultural contents between two versions. In order to implement these goals, a qualitative method based on descriptive content analysis is employed to analyze the presentation and proportion of cultural contents in two sets of English textbooks followed by a detailed examination of similar topics from the two different versions. The findings indicate that the old English textbook included a very limited frequency of occurrences of the cultural representations in both cultural types and cultural dimensions in comparison with the new version of the textbooks. There is an imbalance in both cultural types and cultural dimensions in the old version since culture is mostly introduced with culturally superficial materials. In the new English textbooks, there is still a sharp imbalance in cultural types while still not paying enough attention to the target culture and international culture with the predominance of proportions of neutral culture and source culture but there is a balance of proportions of cultural dimensions with high proportions of practices and perspectives. Moreover, the results obtained by analyzing cultural content by topics clearly show the change in cultural content between two versions. The representations of cultural contents in the new textbooks are more specific, diverse, and deeper than the old textbooks, due to a much higher occurrence of customs, habits, beliefs, and perspectives. In other words, the authors of the newer textbooks have made new strides by introducing broader and deeper cultural content. Therefore, we can suggest that this research contributes to clarifying and supplementing the process of perfecting new English textbooks for Vietnamese students at upper secondary school.