The illiterate was the adult who did not have the opportunities to go to school and could not write and read a letter. Recently, the concept of illiteracy have contained not only basic literacy but also functional literacy. In this stream, the hierarchical-structured ability has been focused by lots of researchers in many countries not in Korea. The purpose of this study was to compare the ability of hierarchical structures and list-structure between the illiterate and the literate. For the purpose, quantitative data were collected from the illiterate and the literate. Also qualitative data were collected from the illiterate who participated the quantitative tests. Quantitative analyses and content analyses of interview data were used. The results were as follows. First, the illiterate’s points and times of hierarchical-structured ability were lower and longer than the literate. Second, the points of list-structured ability did not show any difference. But the illiterate’s examination times for list-structure ability were longer than the literate’s. Third, The qualitative analyses showed that the illiterate could not understand and have some problems for using hierarchical-structured ability. Based on these results, we discussed and suggested the implications.