The distribution equilibrium between coal tar oil fraction (temperature range of distillate: 240 ℃~265 ℃) and solvent was measured by using aqueous solution of 13 kinds as extraction solvent. The aqueous solution of formamide was found to be an optimum solvent for extracting nitrogen heterocyclic compounds (NHC) such as indole contained in coal tar oil fraction based on the distribution coefficient and selectivity. As the results of the use of the aqueous solution of formaide, both an indole yield of 41.1% and a selectivity of 33.3 for indole in reference to 2-methylnaphthalene were obtained through one stage of a batch equilibrium extraction operation.