In this study, it is aimed to develop a valid and reliable achievement test for the subject of "Cell" belonging to the 6th grade "Systems in our Body" unit within the scope of Science course. The achievement test was prepared as a 25-item multiple-choice test, considering the cell-related objectives in the 6th grade Science curriculum. The pilot study of the test was carried out with 62 students attending 6th grade in 2017-2018 academic year. The comprehensibility and the consistency with the scientific knowledge of the test items were prepared by the opinions of various experts in the field of science education. The item analysis was performed according to the answers of the students in the achievement test, and the discriminant and difficulty indexes were calculated for each item. After the item analysis, 3 items were excluded from the test and a Cell Achievement Test (CAT) consisting of 22 questions was obtained. The mean item difficulty of CAT was 0.652 and the mean discrimination index was 0.507.