An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) for the herbicide haloxyfop-P-methyl is reported. Two haptens of haloxyfop-P-methyl with different spacer-arm lengths were synthesized, to which polyclonal antibodies were obtained by immunizing New Zealand rabbits. The most sensitive combination of antibody/coating antigen was selected by homologous and heterologous assays. The results indicated that the spacer-arm length of hapten can affect assay sensitivity. The optimized ic-ELISA showed that the 50% inhibitory concentration (IC(50)) was 0.0419 mg/L, and the limit of detection (LOD) was 0.0019 mg/L. Recoveries were obtained from the agricultural samples, including water, soil, cucumbers, cabbages, tomatoes, and potatoes; all were in the range of 87.4%-111.8%, well within the requirements of residue detection.