Emulsifiable concentrates (ECs) are one of the most widely used pesticide formulations because they have a lot of advantages, such as good storage stability, relatively high biological activity, easy weighing, easy production, and so on. An EC is normally prepared by dissolving a pesticide in a nonpolar solvent with surfactants. When a pesticide is hardly soluble in a common nonpolar solvent, a polar solvent is used as a co-solvent. One of the preferred polar solvents, which have been used for this purpose is N-methyl-2-pyrrolidone (NMP). However, because of its toxic profile, which has recently become apparent, the commercial use of NMP is recently restricted in many fields. Under the circumstances, it is desirable to look for an alternative solvent in the pesticide formulation area. The organic conceptual diagram was tried to search for the alternative solvents because it is a useful tool for predicting the physico-chemical properties of an organic compound. In the organic conceptual diagram, the physico-chemical properties are expressed by the combination of the organic value (OV) and the inorganic value (IV). According to the theory, organic compounds that have similar IV∕OV ratios (the inorganic organic balance = IOB) are mutually miscible in each other. In order to investigate the applicability of this concept to search for a suitable solvent for a pesticide that is hardly soluble in nonpolar solvents, the relationship of the IOB between two hardly soluble pesticides (i.e., a neonicotinoid insecticide and an herbicide) and several types of solvents was evaluated. As expected, solvents having an IOB close to the targeted pesticide showed high solvency against it, while the pesticide did not dissolve in solvents, which have an IOB farther off. It was demonstrated that the organic conceptual diagram can be a good tool for the selection of a solvent for a pesticide that is hardly soluble in the usual nonpolar solvents.