Abstract One role of optimism is to examine how students solve problems in learning mathematics. However, there is still limited research that reveals students’ optimism in posing mathematical problems. This study aims to describe the dimensions of students’ optimism in the mathematical problem posing. This research employed a qualitative method. The research subjects consisted of four Year 8 students (two low-achieving and two middle-achieving students in posing a problem) of one Islamic junior high school in Pidie Jaya, Aceh, Indonesia. The subjects were selected purposively based on their ability to raise problems related to the rectangular pyramid topic. To examine the dimensions of students’ optimism, the researchers interviewed the subjects by referring to optimism indicators proposed by Seligman: permanent bad-events, pervasive bad-events, personal bad-events, permanent good-events, pervasive-good events, and personal good-events. The results showed that: (1) although students have the same problem-posing abilities, they were in a different dimension of optimism, (2) students who had moderate problem-posing abilities were more optimistic than students with low problem-posing abilities, (3) students who had low or moderate problem posing skill tend to be in the pervasive bad event-dimension. In summary, optimism affects the students’ ability to pose mathematical problems.