Student's ability to use and manipulate scientific concepts has been widely explored; however there is still a need to define the characteristics and nature of science ability. Also, the tests and performance scales that require minimal conceptual knowledge to measure this ability are relatively less common. The aim of this study was to develop an objective measure of science ability of gifted middle school students. In order to assess this ability, Science Ability Test Battery was developed by the researchers. The test battery was divided into two sub scales containing; a multiple choice questions achievement test (Science Ability Test) and a performance assessment (Science Performance Test). The initial Science Ability Test consisted of 23 multiple choice items with one correct answer that required students to use science process skills and reasoning. In the study, stratified sampling was used. The test was administered to 280 middle school students in Turkey and the missing data from 26 students were excluded. In order to obtain a proof of content validity, the researchers elicited feedback from five experts in the field of science education and gifted education and necessary corrections were made in accordance of their views and suggestions. This study will be followed by another research to further analyse validity and reliability of the test.