The study aimed to determine students' opinions about their ninth grade biology textbook that had been created in accordance with the constructivist learning approach. On the basis of a detailed literature review of studies on textbooks; questionnaires used for assessment of textbooks; and constructivist learning approach, a questionnaire was created and administered to 751 students from 9 schools located in the city of Trabzon. The questionnaire was classified into the following sections: contents, learning-teaching activities, assessment and evaluation activities, and physical design. The Cronbach's alpha reliability coefficient was 0.94, and the data were analyzed using SPSS 15.0. Multiple findings pertaining to each section were obtained. Overall, it was found that the students were satisfied with their ninth grade biology textbook. While the existence of various visuals was being appreciated by most of the students, some aspects of the textbooks should be developed in order better to support constructivist learning in classrooms. The study also revealed that the questionnaire developed might be used to evaluate textbooks in terms of their appropriateness to constructivist learning theory. The findings of the study are expected to contribute to improving design for future textbooks.