This study was designed to examine predictors of instructional beliefs related to problem solving that influence mathematics in-service teachers' practices in the Chilean context. A total of 713 in-service mathematics teachers from various elementary schools participated in the survey study during 2015 and 2016. Results showed that teachers' traditional beliefs are directly associated with their teacher-centered practices, while there was an indirect relation among reformed beliefs and student-centered practices through teachers' self-efficacy beliefs and their beliefs about the value of problem solving. This association among beliefs and practices suggests that educators and policy makers should be aware of, when designing a teacher professional development, the need to emphasize other variables such as teachers' self-efficacy and value of the task.