Mathematical creativity instrument is a tool to assess students' creative thinking skills in solving mathematical problems. Mathematical creativity has a pivotal role in improving the quality of life, solving problems, making a change, and increasing the efficiency and effectiveness of a system. Unfortunately, there is a gap in the assessment of mathematical creativity in Indonesia because the instrument used is merely confirm teachers' explanation through mathematical problem which focuses on measuring students' knowledge. Therefore, it is necessary to prove the construct validity of the items in the instrument of mathematical creativity assessment. Based on the concept, there are 3 aspects used in creating mathematical creativity instruments, i.e. fluency, flexibility, and originality. This study aimed at examining the construct validity of the instrument. This study used a design and development model. The data were obtained from testing 313 junior high school students in Indonesia. The data were analyzed using Confirmatory Factor Analysis (CFA), using Lisrel 8.80 software through the first-order and the second-order stages. The results show that of all items, totally 15 items, are valid or uni-dimensional with TValue at the value of the loading factor >1.96. This finding proves that unidimensional data parameters can measure the constructs of mathematical creativity and have a significant effect.