In previously published articles, we evaluated the toxicity of four organophosphate (OP) pesticides (dichlorvos, dimethoate, acephate, and phorate) in rats using metabonomic technology at their corresponding no observed adverse effect levels (NOAELs). The results show that a single pesticide did not elicit a toxic response. The joint toxic action of four pesticides (at their corresponding NOAELs) was evaluated by metabolomic analysis of rat plasma under experimental conditions similar to those of the four single OP pesticides. The pesticides were administered daily to rats through drinking water for 24 weeks. The mixture of four pesticides showed a joint toxic action at the NOAELs of each pesticide. The 19 metabolites were statistically significantly changed in all the treated groups compared with those in the control group (p < 0.05 or p < 0.01). Exposure to OP pesticides resulted in increased lysoPC (15 : 0/0 : 0), lysoPC (16 : 0/0 : 0), lysoPC (O-18 : 0/0 : 0), lysoPC (P-19 : 1(12Z)/0 : 0), lysoPC (18 : 1(9Z)/0 : 0), lysoPC (18 : 0/0 : 0), lysoPC (20 : 4(5Z, 8Z, 11Z, 14Z)/0 : 0), lysoPE (16 : 0/0 : 0), lysoPC (17 : 0/0 : 0), 4-pyridoxic acid, glutamic acid, glycocholic acid, and arachidonic acid, as well as decreased C16 sphinganine, C17 sphinganine, phytosphingosine, indoleacrylic acid, tryptophan, and iodotyrosine in rat plasma. The results indicate that the mixture of OP pesticides induced oxidative stress, liver and renal dysfunction, disturbed the metabolism of lipids and amino acids, and interfered with the function of the thyroid gland. The present plasma results provided complementarities with our previous metabolomic analysis of the rat urine profile exposed to a mixture of four OP pesticides, and also contributed to the understanding of the mechanism of joint toxic action.