This study has led to the development of the "Bioethical Values Inventory" that can be used to reveal secondary school students' ethical values in decisions that they make during ethical debates regarding the application of biological sciences. An original inventory development model was used, consisting of four steps and involving qualitative as well as quantitative data collection processes in line with the objectives of the study. In the first step of this model an analysis of ethical debates on biological sciences was followed by the statement of the inventory topics. In the second step, scenarios were created on the ethical dilemmas related to each chosen topic. In the third step, these scenarios were applied to ninth graders (n = 493) in 18 secondary schools in eight districts of Ankara, Turkey. The students' responses to the scenarios were revealed through content analysis strategies and the inventory was converted into a multiple-choice questionnaire through thematic coding. In the fourth step, the inventory was finalized by gathering experts' and students' views on the multiple-choice items. The final version of the inventory and its importance for science/bioethics education is discussed in the light of the relevant literature.