The aim of this study is to develop a rubric to assess mathematical reasoning competence. Since the aim is to assess a competency, the frameworks of the PISA exams in the literature, which give an important place to competencies, have been examined. Due to its focus and in-depth analysis of mathematical reasoning, each of the actions expected from the mathematical reasoning process in the PISA 2021 Mathematics Framework was handled as a criterion and a rubric was created. Data were collected from 30 mathematics teachers with the data collection tool consisting of questions that were stated to be suitable for assessing mathematical reasoning skills in the resource presented as a broadened perspective for the PISA 2021 Mathematics field. The collected data were analyzed using the finalized rubric. In reliability analysis; The "percentage of agreement" among researchers was used to determine the criteria included in the rubric and to be followed with the data collection tool, "Cohen's kappa coefficient" and "Krippendorff's alpha coefficient" methods were used for the agreement between the raters after the analysis of the collected data. The findings show that the Reasoning Competence Rubric (RCR), which consists of 12 criteria, is valid and reliable.