Ill-structured problems can be regarded as one of the measures that meet recent social needs emphasizing students' abilities to solve real-life problems. This study aimed to analyze the mathematical abstraction process in solving such problems, and to identify the mathematical abstraction level ([I] Recognition of mathematical structure through perceptual abstraction, [II] Application of mathematical structure recognition through internalization, and [III] Formation of new mathematical structure recognition through interiorization) and form of the students, by applying ill-structured problem-solving activities to problem-solving learning approaches for fifth grade elementary school students. The study results showed that 2 out of 6 groups displayed the highest level [III] of mathematical abstraction, while two other groups displayed Level [I], and the other two groups showed Level [II]. Especially, the students in each group showed higher levels and forms of mathematical abstraction (from Level [I] to [II] and [III]) over the course of the problem solving process. These study results showed that the mathematical abstraction levels and forms of the students can be improved by exposure to mathematical abstraction through a problem solving learning approach using ill structured problems.