Abstract: This design, fabrication and test of a 0.1 THz fundamental finline single-balanced mixer circuit on a single quartz substrate was presented. The local oscillator(LO) input signal was feeded from WR10 waveguide to a suspended microstrip line, the radio frequency(RF) input signal was also feeded from WR10 waveguide to a finline, and the intermediate frequency(IF) signal was taken to the output port through a LO-IF duplexer. This novel mixer circuit can omit a complex W-band filter compared to traditional mode. The circuit features simple design and easy assemblage. A pair of flip-chipped diodes rested on the 75 m thick quartz substrate, which could improve the size precision of circuit, constitute the basic balanced mixing circuit. After the mixer circuit is fabricated, it owns a 90-110 GHz operating frequency, and its single side band conversion loss is better than 9 dB when the IF is fixed at 50 MHz.