K2CO3-SBA-15 with different K2CO3 content was prepared by thermal dispersion. The structures of resultant powders were characterized by XRD, N2 adsorption and IR. The humidity sensing properties of the powders were also investigated. Compared with pure SBA-15, K2CO3-SBA-15 shows improved humidity sensing properties and the introducing level of K2CO3 has a great influence on the humid sensitivity of K2CO3-SBA-15 composites. The optimal mixing ratio was K2CO3-SBA-15 (0.8 g/g), which exhibited excellent linearity in the whole range of 11–95%RH, a resistance variation of about five orders of magnitude, and a rapid response time and recovery time about 15 and 50 s, respectively. The mechanism of the humidity sensitive properties was also discussed.