The high sensitive dynamic reaction cell inductively coupled plasma mass spectrometry (DRC ICP-MS)-based immunoassayusing ferrocene (Fc) tethered hydroxysuccinimide ester as label for the determination of 2,4-dichlorophenoxyacetic acid(2,4-D) was presented. Ferrocene tethered hydroxysuccinimide ester was directly or via horse radish peroxidase (HRP) as abridge coupled to monoclonal antibody (mAb) of 2,4-D. Competitive immunoreactions were completed in microtiter plateand the signal of 56Fe in the bound ferrocene labeled conjugate was detected by DRC ICP-MS. The potentially interfering40Ar16O+ at the iron mass m/z 56 was reduced in intensity significantly by using NH3 as the reaction gas. The optimizationprocess of the immunoassay was greatly simplified in the aid of enzyme linked immunosorbent assay (ELISA) procedure. The2,4-D was determined in the dynamic range of 0.1–1000 ng/ml and the detection limits of the assays using the two ferrocenelabeled conjugates were found to be 0.044 and 0.055 ng/ml, respectively. The relative standard deviation for six measurementswere within 5.5–15.3%.