The objective of this observation is to describe: (1) Teaching materials construction process is based on inquiries aided by multimedia; (2) The construction through Geometry materials in particulars to qualify critical thinking ability of students. This observation apply the tool of Qualitative Descriptive Method Analysis with developed Model 4-D. The targeted subjects were over High School students of 10th who scattered demographically across North Sumatra. The object is is constructing mathematical teaching materials based on inquiries aided by Multimedia. The experimental observation inferred that: (1) the 4-D Thiagarajan encompasses 4 phases, they are definition, design, construction, dissemination; (2) the results are feasible applied because meet the valid criteria, simple and effective. The valid criteria is visible from format aspect, language, illustration and content through expertise assessment. Simplicity criteria emerged from teachers’ activity to prepare the good learning in other hand that teaching materials regarded simple. Meanwhile effectivity criteria perceptible from students’ activity in learning and positive response.