The reaction and poisoning mechanism of organophosphorous gas with LaCoO3 model catalyst have been studied. Organophosphorous gas diffused into LaCoO3 model catalyst and reacted to form some new species such as LaPO4, La-4(P2O7)(3) and CoO, which resulted in the distortion and destruction of perovskite structure. The residual concentration of phosphorus in the catalyst layer reached a maximum after the catalyst was poisoned at 600 ° C for 2 h. The diffusion depth of phosphorus in LaCoO3 layer increased with poisoning temperature and time. After the model catalyst was poisoned at a high temperature above 700 ° C or for a longer period, the distribution of phosphorus in the LaCoO3 layer became homogeneous and the distribution peak of P concentration shifted into the layer. The catalytic performance test for oxidation of CO indicated that the formation of phosphate and the destruction of the perovskite structure in LaCoO3 catalyst layer resulted in the deactivation of the perovskite catalyst. © 2004 Elsevier B.V. All rights reserved.