To enhance the extraction of a contaminant from soil by improving the contact of soil with an extractant by using an extractant having high solvent capacity to a contaminant and adding a very small amt. of a hydrophilic co- solvent to the extractant.

A high b.p. org. contaminant is separated from a compsn. constituted of water of an amt. from 5% to the threshold value of soil water capacity and soil containing the high b.p. org. contaminant. At this time, the compsn. is brought into contact with an extractant mixture consisting of a solvent for fractionating petroleum and a polar co-solvent which are selected so as to be capable of constituting a single liquid phase along with water contained in the compsn. to be mutually mixed. Next, a coarse fraction of soil is separated from a liquid phase containing a fine fraction of soil and, subsequently, the liquid phase is separated from the fine soil fraction. The coarse and fine soil fractions are dried. The contaminant is a polynuclear aromatic substance or an organochlorine compd. and, as the solvent, ethyl acetate is designated and, as the co-solvent, acetone and acetic acid are designated.