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 μm 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.