Purpose: The purpose of this study is to investigate the prospective teachers' ability to write context-based problems about the concepts in radioactivity unit. Methodology: The study is carried out in a university in Turkey with 21 prospective teachers in physics, chemistry and biology in 2014-2015 fall terms. In the study, data are collected through the papers on which prospective teachers write context-based problems about the concepts in radioactivity unit. Data are analyzed with a rubric which is developed by the researchers. Results: Results indicate that prospective teachers are found as "not adequate" at selecting daily life context. Conclusions: At the end of the study, it is revealed that prospective teachers understand the "context-based" concept as "only relating something with daily life." It is suggested that in-service courses may solve and eliminate this problem. Recommendations: It is proposed that in-service courses may provide prospective teachers more experience before being a teacher and there is a need for more and better designed researches. (Contains 2 tables and 4 figures.)