Two layers of cationic iron(III) meso-tetrakis (N-methylpyridinum-4-yl)porphyrin (FeTMPyP) and anionic gold nanoparticles (GNPs) were alternately assembled on a poly(diallyldimethylammonium chloride)-wrapped carbon nanotube (PDDA-CNT)-modified electrode via electrostatic interactions. The porphyrin-functionalized gold nanoparticles were characterized by scanning electron microscopy and UV-vis absorption spectrometry. The (FeTMPyP-GNP) 2 /PDDA-CNT modified electrode showed two stable and well-defined peaks at -0.112 V and -0.154 V, which were attributed to the GNP-accelerated redox process of Fe(III)TMPyP/Fe(II)TMPyP. The modified electrode possessed excellent electrocatalytic behavior for the reduction of peroxyacetic acid (PAA). The resulting biosensor exhibited a fast amperometric response to PAA (∼3 s), with a wide linear range from 2.5 × 10 -6 M to 1.05 × 10 -3 M and a detection limit of 0.5 M at a signal-to-noise ratio of 3. More importantly, H 2 O 2 did not interfere with the detection. Thus, this biosensor enabled highly sensitive detection of PAA without removing H 2 O 2 and showed a promising potential in practical applications.