This work is based on a new structure of transmission line- slotted semi-coaxial line and made on BCB substrate. We compared attenuation constant and other properties with microstrip line and semi-coaxial line in single-ended and differential mode. We also compared the coupling effect between proposed transmission lines and conventional microstrip line. The single-ended slotted semi-coaxial line shows lower attenuation constant by simulation and measurement under same line dimensions. However, differential slotted semi-coaxial line does not show clear improvement in attenuation constant.