Aim To develop monoclonal antibodies(mAbs) against a novel hapten, pinacolyl 1-p-aminophenyl-1-hydroxymethylphosphonate(P4). Methods P4 was coupled chemically with Limulus polyphemus hemocyanin (LPH) to form a coupling agent P4-LPH, and then BALB/c mice were immunized with the P4-LPH. MAbs were prepared by hybridoma technique. Cross reactivities of mAbs to 7 ligands were detected by competitive inhibition enzyme immunoassay. The cross reactiveities were expressed by the concentration of ligand which inhibited 50% reaction of mAbs(IC(50)). Results Nine mAbs were developed. Eight of them were specific for P4, four (1B3, 2B2, 3D5 and 4F1) could react to soman, their IC(50) were 10(-3), 10(-3), 10(-5) and 10(-6) mol/L respectively, and one (4F1) could recognize paraoxon, IC(50) being 10(-5) mol/L. All of which were effective with a titer as high as 10(6) to 10(8) in dilution. Conclusion mAbs specific for soman and paraoxon are developed successfully, which may be used for research on soman abzyme, immuno-detoxification of soman poisoning and immunoassay for soman or/and paraoxon.