Abstract: An external method based on liquid chromatograph-electrospray ionization-mass spectrometry was developed for the determination of low-level residues of four nitrofuran in eel muscle.The procedure entailed an acid-catalyzed release of protein-bound metabolites,followed by the derivation,liquid-liquid extraction,positive electrospray ionization applying multiple reaction and monitoring two transitions for each compound.The standard curve was reliable,the LOQ was 0.5 ng·g-1,the nitrofuran metabolite recovery rates at 5 fortification levels(i.e.,0.5,1.0,2.0,5.0,10.0 ng·g-1) were 70%-130%.The LOD was 0.25 ng·g-1.The method was rapid,simple economical and its LOQ below the minimum performance limit of 1 ng·g-1 set by Japan and the EU.