Abstract: Three different types of high speed materials were respectively processed into PCBs which characterized with the same dielectric layer thicknesses and pattern designs. The dielectric constant Dk and dielectric loss Df of the aforementioned materials under the condition of different temperature humidity were investigated employing temperature humidity chamber and SPDR fixture. Additionally, a comparative study of the insertion loss of 85Ω differential impedance lines corresponding to PCBs based on the aforementioned materials was performed using Vector Network Analyzer. It was found that the Dk and Df of the three different high speed materials increased as the ambient temperature and humidity increased. When the ambient humidity was constant, the insertion loss modulus of 85Ω differential impedance lines increased as ambient temperature became higher, which could be attributed to variations of Dk and Df of high speed materials under different temperatures. And the insertion loss was affected more by Dk than Df.