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