This study was designed to develop an assessment tool to measure high school students' personal epistemology (PE) in the physics domain by using validation processes. Based on theoretical foundations of PE, the PPEQ was conceptualised on six hypothetical dimensions: structure of knowledge [SK], justification of knowledge and knowing [JK], changeability of knowledge [CK], equations in physics [EQ], quick learning [QL], and source of knowledge [source]. In total, 42-items were developed deductively for these dimensions, and a panel of experts assessed the content validity of the instrument. Subsequently, factor analyses were performed to obtain construct-related evidence. First, exploratory factor analysis (EFA) was performed on the data collected from 362 ninth graders. EFA yielded a six-factor solution which excluded the EQ and divided SK into two dimensions: coherent SK and hierarchical SK. Second, confirmatory factor analysis (CFA) was conducted with the remaining 27-items on data collected from a new sample of 350 ninth graders. The CFA results confirmed that the PPEQ assesses six factors emerged from EFA. Internal consistency of the PPEQ was also found to be very high with Cronbach's a reliability coefficient of 0.92, and the coefficients of dimensions ranged from 0.71 to 0.83.