In this study, an immunosensor with a piezoelectric quartz crystal was developed. An oscillator system, in order to measure the frequency shifts caused by the increase of mass on the piezoelectric crystal, was used. The surfaces of the quartz crystals were treated by a glow-discharge technique utilizing ethylene diamine monomer to substitute amino groups on the surface of the crystal. These groups were activated by a bifunctional cross-linker, glutaraldehyde, to immobilize an antibody (so called anti-HBs). Optimum conditions for each of the modification steps for application on the quartz crystal surfaces were established and the results were represented for optimum time, pH and concentration. The sensor was calibrated at optimum conditions for HBs-Ag detection.