Transmission coefficient with amplitude and phase information of four building materials had been measured in the 3.1 to 10.6 GHz frequency band for both polarized waves. A free-space measurement system was setup in a fully anechoic chamber to carry out this measurement. The results show that the variation in transmission coefficient between two polarizations is within 10.3%. And the deviations between different samples for the same material could be evident for some material. Also the different behavior of transmission characterization in this frequency band had been observed for different material. These characterizations would be important factors in UWB channel modeling and analysis.