This study aimed to develop the blended learning design using the Kelase platform with learning concepts that internalize the Tri Kaya Parisudha concept and the Mathematics material structure by using Superitem concept so that the Mathematics learning process at the level of high school or vocational can be more effective. This research was carried out with a development research approach using the Borg and Gall model with the main focus of development at the design development stage. Subjects involved in the development of the design were three researchers; the initial design trial was four experts and 30 Mathematics teachers. Data collection tools in the form of questionnaires, interview guidelines, and photo documentations. The technique used to analyze the data was quantitative descriptive. The results showed that the effectiveness of the blended learning design that had been developed was classified as good common with an average effectiveness percentage of 88.76%. Based on that effectiveness percentage was compared to the five-scale categorization, it's recommended not to do a major revision of the blended learning design.