The stability of 89 pesticides (17 organochlorine, 33 organophosphorus, 8 pyrethroid, 12 carbamate, and 19 other pesticides) in 6 kinds of organic solvents (methanol, ethanol, 2-propanol, ethyl acetate, n-hexane, and acetone) was investigated using gas chromatography/mass spectrometry (GC/MS). All of the investigated pesticides were stable in all of the tested organic solvents during storage for 6 hours at room temperature in the dark except captafol, captan, phosmet, chinomethionat, and dicofol. However, the decreases of captafol, captan, phosmet, and chinomethionat were observed in methanol. The decreases of captafol, captan, and phosmet were also observed in ethanol. Moreover, the decrease of dicofol was observed in acetone. The decrease of captafol dissolved in methanol at a concentration of 2 micrograms/ml was faster than those of captan, phosmet, and chinomethionat; the residual captafol was 75% after 30 min of storage. Dicofol dissolved in acetone also decreased during storage in a refrigerator. 4,4'-dichlorobenzophenone (DCBP) and chlorobutanol were detected in the acetone solution of dicofol after storage. Furthermore, it was found that dicofol was decomposed by acetone at an injection port, and DCBP and chlorobutanol were formed when it was injected into GC with acetone.