A tin dioxide (SnO2) thin film was prepared by metallorganic chemical vapor deposition from a tetramethyl tin (Me4Sn) precursor. The characterization of gas-sensing properties of trimethylamine (TMA) was reponed. The film was almost insensitive to TMA. When doped with thorium, it was very sensitive to TMA gas of very low level at working temperatures ranging from 200 to 360 degrees C, and the response and recovery times were very short. The optimum range of the working temperatures was from 270 to 310 degrees C, which was very low as compared with calcined mixed powder of SnO2 and ruthenium. The concentration range of gaseous TMA of linear response was 10-300 ppm.