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The success of a lesson in school cannot be separated from the teacher's assessment system. However, current assessments cannot be used as a measure of learning success because most teachers only assess them from a cognitive perspective. Basic competency assessment is carried out based on indicators of achievement of learning outcomes, both in the form of cognitive, affective, and psychomotor domains. For this reason, an assessment that is very suitable for making such an assessment is an authentic assessment. This study describes the process and results of the development of authentic assessment tools in geometry for middle-school students. The teaching material development model refers to the 4-D Thiagarajan model has 4 stages, including definition, design, development, and dissemination. These learning participants, were distributed to students public junior high schools, in Gowa, South Sulawesi. The research data were obtained by using validation sheets, teacher and student activity observation sheets, student response questionnaires, and learning outcomes test sheets. The product of this research is an authentic assessment tool in geometry. The results showed that the authentic assessment was valid, practical and effective. Therefore, as an implication obtained from this assessment, it is suggested that the development of authentic assessment tools in learning geometry should also be developed in other materials in order to assist teachers in assessing students based on the abilities that students have.