Polyclonal antibody (PAb) with broad-specificity for O,O-diethyl organophosphorus pesticides (OPs) against a generic hapten, 4-(diethoxyphosphorothioyloxy)benzoic acid, was produced. The obtained PAb showed high sensitivity to seven commonly used O,O-diethyl OPs in a competitive indirect enzyme-linked immunosorbent assay (ciELISA) using a heterologous coating antigen, 4-(3-(diethoxyphosphorothioyloxy)phenylamino)-4-oxobutanoic acid. The 50% inhibition value (IC50) was 348 ng mL(-1) for parathion, 13 ng mL(-1) for coumaphos, 22 ng mL(-1) for quinalphos, 35 ng mL(-1) for triazophos, 751 ng mL(-1) for phorate, 850 ng mL(-1) for dichlofenthion, and 1301 ng mL(-1) for phoxim. The limit of detection (LOD) met the ideal detection criteria of all the seven OP residues. A quantitative structure-activity relationship (QSAR) model was constructed to study the mechanism of antibody recognition using multiple linear regression analysis. The results indicated that the frontier-orbital energies (energy of the highest occupied molecular orbital, E(HOMO), and energy of the lowest unoccupied molecular orbital, E(LUMO)) and hydrophobicity (log of the octanol/water partition coefficient, log P) were mainly responsible for the antibody recognition. The linear equation was log(IC50) = -63.274E(HOMO) + 15.985E(LUMO) + 0.556 log P-25.015, with a determination coefficient (r2) of 0.908.