Among students, the indispensable element of learning motivation arises from their beliefs of positive values. The Mathematical Beliefs Scale (MBS) was developed to address the mathematics study needs of Taiwan junior high school students. For cross validation, there were two major stages, a pre-test questionnaire was then developed, and purposive sampling was used to select 114 students to participate. Reliability under the Cronbach's α was 0.850. Finally, 639 students were selected using random sampling to participate in the official questionnaire, and a confirmatory factor analysis (CFA) was conducted. The results demonstrated good reliability and validity.