This research is generally aimed at underlying context, input, process, product of assessment system at Institute of Foreign Language Development of Nurul Jadid Islamic boarding school Paiton Probolinggo. The type of this research is ex post facto evaluation using mix method approach. The data was collected using observation, documentation, interview, and verification of virgin as well as descriptive statistical analysis. The result indicated that; 1) context evaluation in the evaluation system at Institute of Foreign Language Development of Nurul Jadid Islamic boarding school is generally categorized as adequate, 2) input evaluation in the assessment system at Institute of Foreign Language Development of Nurul Jadid Islamic boarding school is categorized as adequate, 3) process evaluation in the assessment system at Institute of Foreign Language Development of Nurul Jadid Islamic boarding school in term of its process in general is generally categorized as lacking, 4) product evaluation using passing grade (KKM) 75 resulted that out of the thirteen classes managed by Institute of Foreign Language Development of Nurul Jadid Islamic boarding school, many of its students receive score below KKM, there are only two out of those thirteen classes who receive score above KKM or in other word there are only two classes whose students are categorized as “passing”. Therefore, in term of its product, there are two that are categorized as lacking in the assessment system at Institute of Foreign Language Development of Nurul Jadid Islamic boarding school.