Label-free detection of bisphenol A based on the impedance measurement was achieved with an impedimetric immunosensor. The immunosensor was fabricated by the covalent bond formation between a polyclonal antibody and a carboxylic acid group functionalized onto a nano-particle comprised conducting polymer. By using a commercial reagent 4,4-bis(4-hydroxyphenyl) valeric acid (BHPVA), which has an analogous structure of BPA, we have prepared the antigen through the conjugation of BHPVA with bovine serum albumin (BSA) and then produced a specific polyclonal antibody. The immobilization of antibody and the interaction between antibody and antigen were studied using quartz crystal microbalance (QCM) and electrochemical impedance spectroscopic (EIS) techniques. The impedance and mass changes due to the specific immuno-interaction at the sensor surface were utilized to detect antigen and bisphenol A (BPA). The immunosensor showed specific recognition of BPA with less interference than 4.5% from other common phenolic compounds. Under an optimized condition, the linear dynamic range of BPA detection was between 1 and 100 ng/ml. The detection limit of bisphenol A was determined to be 0.3+/-0.07 ng/ml. The proposed immunosensor was applied to a human serum sample and the BPA concentration was determined by the standard addition method.