This study aimed to develop a valid and reliable multiple-choice achievement test for the subject area of ecology. The study was conducted within the framework of exploratory sequential design based on mixed research methods, and the study group consisted of a total of 250 middle school students studying at the sixth and seventh grade level. In the process of preparing the question pool, the level and scope of the questions in the pool were shaped by taking into account the achievements of science, environmental education and climate change courses. A question pool consisting of questions obtained as a result of the literature review and prepared by the researcher was created. The pool of 41 questions was reduced to 29 questions in line with expert opinions. The 29-question multiple-choice test, whose language comprehensibility was examined and necessary arrangements were made, was made ready for implementation. The draft form of the achievement test, which was piloted, was applied to 250 students. Item difficulty indices and item discrimination indices of the test answers obtained from the students were calculated. After the item analysis, a total of 4 questions were removed from the test. As a result of the analyses, the average difficulty value of the test was calculated as 0.58 and the average discrimination value was calculated as 0.60. The KR-20 reliability coefficient of the developed test was 0.85 and Cronbach alpha reliability coefficient was 0.88. As a result of the research, a valid and reliable ecology achievement test was developed.