Abstract: The absorbing EMW properties and mechanical properties of cement-based composites, which are made of portland cement and nanometric absorbing materials, were studied. The relation-ship between electromagnetic wave reflectivity and nanometer TiO₂ contents, dispersed means, samplesthickness were discussed and analysed. And nanometer titanium oxide effect on mechanical propertiesof cement-based composites were discussed. The experiment data show that reflectivity of cement-based composites with nanometer titanium oxide is less than -7dB in 8～18GHz frequency range.The minimum reflectivity is -16.34dB at 16.24GHz, and bandwidth for -10dB is 4.5GHz. Itsmechanical properties precede cement paste.