Summary writing is essential for academic success, and has attracted renewed interest in academic research and large-scale language test. However, less attention has been paid to the development and evaluation of the scoring scales of summary writing. This study reports on the validation of a summary rubric that represented an approach to scale development with limited resources out of consideration for practicality. Participants were 83 students and three raters. Diagnostic evaluation of the scale components and categories was based on raters' perception of their use and the scores of students' summaries which were analyzed using multifaceted Rasch measurement (MFRM). Correlation analysis revealed significant relationships among the scoring components, but the coefficients among some of the components were over high. MFRM analysis provided evidence in support of the usefulness of the scoring rubric, but also suggested the need of a refinement of the components and categories. According to the raters, the rubric was ambiguous in addressing some crucial text features. This study has implications for summarization task design, scoring scale development and validation in particular.