This paper describes the conception and the development of an immunosensor for the ochratoxin A (OTA) detected by electrochemical impedance spectroscopy (EIS) coupled with a quartz crystal microbalance (QCM). The immunosensor was constructed by immobilizing antibodies against OTA on a mercaptoundecanol/mercaptoundecanoic acid (MU/MUA) mixed self-assembled monolayer (SAM)-modified gold electrode. The antibody-antigen interaction was investigated by EIS and the stability of the system was monitored by QCM. The charge transfer resistance changes were interpreted in term of electronic transfer rate changes rather than in term of surface coverage. This idea was corroborated through microbalance measurements. Endly, the increase of the relative change of charge transfer resistance (Delta R-ct/R-ct(o)) is proportional to OTA concentration and linear between 100 and 1000 pg.mL(-1).