Creative Mathematically founded Reasoning meets three criteria, namely Creativity, Plausibility, and Anchoring. Creative Mathematically founded Reasoning is very important because the students can solve problems, think logically, solve problems in their own way, and develop creativity. Creative Mathematically founded Reasoning required students not only solving the problems by using formulas or rules given but also understanding why they should solve the problems and how to solve in new and reasonable ways. Nevertheless, most of the students still use algorithmic reasoning so that impact to their performance in solving the problems. It happens because someone with a lower memory capacity get difficulties to choose and process the information that is in accordance with the need to solve the problem. Working memory is needed in processing information and taking back the information needed in long-term memory, so that working memory capacity becomes a much needed in Creative Mathematically founded Reasoning. Based on the background, this study aims to study Creative Mathematically founded Reasoning of prospective teachers in solving problems that are reviewed based on their working memory capacity. It is a qualitative research that was conducted at Universitas Kristen Indonesia Toraja, South Sulawesi in the Mathematics Education Department. Operation Span (O-SPAN) Task was used to select the research subjects which are 1 student with a high category working memory capacity and 1 students with a low category. After the selection, subjects were given a test to see their Creative Mathematically founded Reasoning. Based on the data analysis it can be concluded that students working memory capacity are different so that their Creative Mathematically founded Reasoning in solving mathematics problems.