The curriculum reform implemented in Croatia in 2019 and 2020 resulted in significant changes in the curriculum of the subject biology, which were reflected in changes in the content and structure of biology textbooks. Since several years have passed since the introduction of the reform, the purpose of this study is to investigate the attitudes of high school students and teachers toward biology textbooks. 165 students and 44 teachers from high schools in the Republic of Croatia participated in the survey. An online questionnaire was used as an instrument for data collection. The results show that the majority of students believe that the textbook is well suited for self-study and that they do not find it difficult to learn from the textbook, but their opinions are divided on the way the topics are covered and on the connection and logical sequence of the content in the textbook. Teachers express dissatisfaction with the clarity and systematic nature of textbooks, pointing out that content is not logically linked and that textbooks are often not aligned with the curriculum. In addition, they frequently indicate that textbooks from different publishers can have completely different content outlines, which in some cases greatly affects the quality of the textbooks and students' ability to use them independently. The majority of teachers are particularly dissatisfied with the structure of the 2nd grade biology textbook. The results of this study point to the need to constantly monitor the quality of the biology textbooks and improve them according to the specific suggestions of the teachers and students who use them.