Metacognitive self-regulation is the ability to organize an individual's mental activities according to his/her goals, and it has been found to affect students' mathematics achievement. However, its relationship with problem-solving and posing skills is still not clarified. This study aims to examine the mediating role of metacognitive self-regulation skills in the relationship between primary pre-service teachers' problem-posing skills and mathematics achievement. Participants consist of 165 primary pre-service teachers studying at different grade levels in the Primary School Teaching Department. The data were collected with the metacognitive self-regulation scale and the problem-posing test consisting of semi-structured problem-posing questions. The proposed hypothesis regarding the role of metacognitive self-regulation in the relationship between problem-posing and mathematics achievement in the study was tested by structural equation modeling and confirmed by bootstrap analysis. Analysis results revealed that problem-posing and metacognitive self-regulation significantly predicted mathematics achievement, but metacognitive self-regulation was not a significant mediator between problem-posing and mathematics achievement.