A simple and signal-amplified, label-free electrochemical impedimetric immunosensor for dibutyl phthalate (DBP), a type of phthalate ester, was developed using gold nanoparticles (AuNPs) induced signal amplification. The approach was based on an indirectly competitive binding system of coating antigen that coated on antigen/chitosan/[email protected]/GCE (modified electrodes), target (DBP) and anti-DBP antibody. Signal amplification was performed via the enlargement of AuNPs through NADH-promoted catalytic precipitation, which caused a marked increase in the electron-transfer resistance and electrostatic repulsion after an AuNP-labeled second antibody conjugated to anti-DBP. Under the optimized conditions, this method displayed: (i) low detection limits (7ng/mL, 10 times lower than the traditional ELISA method using the same antibody); (ii) satisfactory accuracy (recoveries, 86.0-120.4%) and agreement with corresponding ELISA method; (iii) high tolerance to some environmental interferents; and (iv) low cost and low sample consumption (6µL). Our results demonstrate the great potential and high efficiency of this immunosensor in practical applications for the cost-effective and sensitive monitoring of DBP in aquatic environments.