In this research, interactive multimedia on thermodynamic concepts was developed and tested. The purpose of this research was to assess the effectiveness of interactive multimedia through a problem-based learning approach to students' critical thinking disposition. The research development had three stages: preliminary study, development, and field testing. The field testing was a quasiexperiment with a pretest and posttest control group design. The research subjects consisted of four lecturers as expert validators, two teachers and two groups of 65 students in a high school in Mataram city, Indonesia. Data were gathered by using questionnaires, observation, interviews, and written test. The results of the Normalized-gain test were 53.1 for the experiment group and 52.2 for the control group. This shows that there were differences in the increase of students' critical thinking dispositions between the control group and the experiment group. Therefore, it can be concluded that the application of interactive multimedia could improve students' critical thinking dispositions.