This study was conducted to find out the opinions of lecturers and students about the teaching-learning contents in the textbook “Active Skills for Reading 4” used to teach Reading Skills level 6 to third-year students majoring in English at Hanoi Open University. The author used a mixed research method, combining quantitative and qualitative research methods to analyze data. The list of textbook evaluation checklists compiled by Litz (2005) and the authors Mukundan, Nimehchisalem, and Hajimohammadi (2011), after being edited to suit the research object, is used as the main research tool. Eight lecturers and eighty-four third-year students majoring in English at Hanoi Open University participated in the study, and two teachers were invited to participate in interviews to clarify some information. The data collected revealed that most surveyed lecturers and students highly appreciated the diversity of topics, their interest in reading comprehension, and the clarity of instructions for the exercises in the textbook Active Skills for Reading 4. However, the criteria for the diversity of question types, quantity and variety of vocabulary, and way of introducing vocabulary are not highly appreciated. Based on the findings, the interviewed lecturers made some recommendations on how to use this textbook more effectively. The study has helpful theoretical and practical contributions to textbook selection, evaluation, and effective use of textbooks.