The aim of this study is to reveal relations between creativity in design and the cognitive developmental stages of designers within a Post-Piagetian approach. In this study design processes were deeply inspected with the aim of obtaining more comprehensive information about the effects of individual’s cognitive status on the design processes, problemsolving and quality of idea generation . In this field, studies done so far have been conducted on test results as indicators of creativity. Withinthe present study, however, protocol analyses were also evaluated, in addition to test results, and thanks to this addition, it was possible to determine the qualitative and quantitative effects of cognitive developmental stages on creativity. A total of twenty-five students voluntarily participated in the research. To collect data, two different methods were employed. The Social Paradigm Belief Inventory (SPBI), was employed to determine students' cognitive stages and scores, and the Think-aloud protocol was used to elicit verbal reports of the thought sequences of the students. In order to analyse the verbal reports reflecting designers' cognitive activities, the method of Linkography was conducted and the general statistics of segments were measured. To assess the relations between creativity in design and the cognitive developmental stages of the designers, SPBI scores and the general statistical values obtained from the design sessions were correlated. Findings showed that there is a strong and significant correlation between the cognitive development levels and creativity, in favour of dialectical thinking.