A new material-poly{methyl [3-(2-hydroxyl, 4,6-bistrifluoromethyl)phenyl]propylsiloxane} (PMTFMPS), which was sensitive to toxic organophosphate vapor, was synthesized via O-alkylation, claisen rearrange reaction and hydrosilylation reaction. The polymer was coated on quartz crystal microbalance (QCM) to investigate its gas sensitive properties to nerve agents' simulant dimethyl methylphosphonate (DMMP) vapor, as well as other interfering vapors. It was found that QCM sensor responded linearly to DMMP vapor with a slope of 27 Hz/ppm in the 10-50 ppm range. The material was much more sensitive to DMMP than to other interfering vapors, thus high selectivity to DMMP was demonstrated. The influence of humidity on the sensor response was also examined. The results showed that the frequency shifts were about 60% when tested in 77% RH wet air than in dry N-2. When compared with our previously studied unfluorinated phenol-modified siloxane PMPS, PMTFMPS exhibited sensitivity enhancement of 2.3 times and an increased resistance to humidity variations.