||Since the ultralow dielectrics are tobe applied to system LSI as interlayers, they must satisfy such properties as dielectric properties and mechanical strengths. In addition, plasma induced damage (PID) resistance is very important issue for their processing. We have developed the ultralow dielectrics (k ＜ 2.0 and E = 7.2 GPa) by using the copolymer of methyl trimethoxy silane and 1,2-bis(triethoxysilyl)ethane as a matrix and trimethoxysilyl xylitol (TMSXT) as a reactive porogen. To further enhance PID resistance of the ultralow dielectrics, we synthesized two kinds of organosilicate matrices by substituting the second monomer with 1,3-bis(triethoxysilyl)propane (BTESP) and 1,4-bis(triethoxysilyl) butane (BTESB). We obtained new ultralow dielectrics with k = 2.21 and k = 2.31 by introducing TMSXT (50 vol%) into the new organosilicate matrices, respectively. PID will be studied as a function of the number of bridged carbon.