Fragmentation is adopted from the term of inefficient data storage in a computer which is used to describe thinking fragmentation. The purpose of this study is to describe the fragmentation of geometrical concepts in junior high school classified into: hole construction, mis-connection, and mis-analogical construction. This study used descriptive qualitative research method with the subjects of 8th grade students in Surakarta. Data collection in this study was conducted by task-based interview method. Qualitative descriptive analysis through the stages of reduction, representation, and interpretation of data. Hole construction occurs when students do not construct concept completely (20%). Mis-connection occurs when students make mistake in making connections between concepts (40%). Mis-analogical construction occurs when students analogizing a concept with another concept in geometry which is a mistake (20%). From the analysis result, defragmentation of thinking structure in geometry can be done with scaffolding to bring up scheme, knite scheme, and improve of analogic thinking.