Piezoelectric membrane, working as resonant device, was introduced as biosensor platform. The principle of this device is based on the frequency response of mass load due to the capture of anthracis spores by phage immobilized on the membrane surface. The responses of membrane in anthracis spores solutions were experimentally studied. It was found that the sensitivity of detection can be improved by using smaller membrane or by using high resonant mode of the membrane, which is in good agreement with the theoretical analyses.