FeS2-MWCNTs (Multi-Walled Carbon NanoTubes) composite without using an organic binder was used as a thin cathode for thermal batteries. A thin cathode with FeS2-MWCNTs composite exhibited good mechanical strength without an organic binder. A discharge evaluation of the thin cathode with FeS2-MWCNTs composite revealed a discharge capacity 2.3 times that of the pellet type cathode and 1.13 times that of a thin cathode with an organic binder. In addition, the single battery applying a thin cathode with FeS2-MWCNTs composite showed a lower total polarization than when applying an organic binder. These results showed that FeS2-MWCNTs composite is suitable as a thin cathode for thermal batteries.