The distribution equilibrium properties (distribution coefficient, yield and selectivity) between the feed of coal tar oil fraction (temperature range of distillate: 240 ℃~265 ℃) and the solvent(aqueous solution of formamide) were experimentally measured with changing various experimental factors and conditions (the moisture content in the solvent, etc.) in order to study the performance of operation and of separation. With increasing the moisture content in the solvent, the distribution coefficients of nitrogen heterocyclic compounds (NHC) and indole decreased and the selectivities of the NHC based on bicyclic aromatic compounds (BAC) and indole based on 2-methylnaphthalene increased. Increasing volume ratio of solvent to feed at initial resulted in increasing the distribution coefficients of NHC and indole increased and the selectivities of the NHC based on BAC and indole based on 2-methylnaphthalene decreased. The process for the separation and recovery of NHC (particularly, indole) contained in coal tar was investigated by using the results obtained from the distribution equlibrium between coal tar oil fraction and aqueous solution of formamide.