This study aimed to determine the improve of conceptual mastery of thermodynamics as result of the implementation of the interactive multimedia thermodynamics. Research method used a quasi-experiment with control group pretest-posttest design. The research subject was students as experimental group and control group of physics prospective teachers of the fourth semester, in one of the state university in East Kalimantan. The research instrument used multiple choice test embedded conceptual mastery of thermodynamics. Data analyzed with the differences of two averages. The result showed that after the implementation of interactive multimedia improved of conceptual mastery of physics prospective teachers quite effectively. These results indicated that the interactive multimedia improve the conceptual mastery of physics prospective teachers.