Geometry subject that prosecute students to comprehend abstracts things is one of the causes of students' difficulties in mathematics learning. This study aims to determine the effect of Problem Posing and Problem Solving learning models with the Scientific Approach to students' adaptive reasoning on plane figure materials. It was conducted at the State Junior High School (SMPN) 4 Magetan, Indonesia. It employed quasi-experimental research methods. The populations were the seventh grade students with a total sample of 64 students who were divided into 34 students as experimental 1 class and the other as experimental 2 class. The simple random sampling method was chosen as the sampling technique. Moreover, normality test was the Lilliefors method; homogeneity was the Bartlett test; and t-test for research results analysis. The results revealed that the Problem Posing learning model with the Scientific Approach was better than Problem Solving with the Scientific Approach. It significantly enhanced students' adaptive reasoning on plane figure materials. The Problem Posing learning model with the Scientific Approach provided the needed skills to build knowledge, where students performed the process of observation, clarification, measurement, prediction, and hypotheses. Therefore, the model was appropriate for mathematics learning, especially on plane figure materials to increase students' adaptive reasoning and achievement.