A flow injection (FI)-electrochemiluminescent (ECL) method has been developed for the determination of gallic acid, based on an inhibition effect on the Ru(bpy)(3)(2+)/tri- n-propylamine (TPrA) ECL system in pH 8.0 phosphate buffer solution. The method is simple and convenient with a determination limit of 9.0x10(-9) mol/L and a dynamic concentration range of 2x10(-8)-2x10(-5) mol/L. The relative standard deviation (RSD) was 1.0% for 1.0x10(-6) mol/L gallic acid ( n=11). It was successfully applied to the determination of gallic acid in Chinese proprietary medicine-Jianming Yanhou Pian. The inhibition mechanism proposed for the quenching effect of the gallic acid on the Ru(bpy)(3)(2+)/TPrA ECL system was the interaction of electrogenerated Ru(bpy)(3)(2+*) and o-benzoquinone derivative at the electrode surface. The ECL emission spectra and UV-visible absorption spectra were applied to confirm the mechanism.