Reflective thinking skills are thought to be an important factor affecting the success of problem solving both routine and non-routine science problems. This research aimed to determine the relationship between eighth-grade students' reflective thinking skills toward problem-solving and their level of solving routine and non-routine science problems. Determining this relationship can form a basis for the decisions teachers make in courses and contribute to increasing teaching quality. A correlational and regressional research design was used in this study. A total of 408 eighth-grade students from four secondary schools in Kocaeli, Turkey, constituted the sample group. The correlational results showed that as the students' reflective thinking toward problem solving scores increased, which were identified as questioning, reasoning, and evaluating, their level of solving routine and non-routine problems also increased. However, multiple regressional results showed only the "evaluation" skill was a significant predictor in solving routine problems and only the "reasoning" skill was a significant predictor in solving non-routine problems. Therefore, students should also be equipped with reasoning skill such as examining the cause-and-effect relationships by investigating the reason behind the decisions made while solving a problem, to contribute to the solution of non-routine problems.