A simple and rapid method (slow-stirring method) for extracting environmental DNA (eDNA) from soils was constructed by physical mild stirring with chemical treatment. eDNA was extracted efficiently with minimal damage from various kinds of soil. The amount of eDNA and soil bacterial biomass showed a linear proportional relation [Y=(1.70x10(8))X, r(2)=0.96], indicating that bacterial biomass could be evaluated by quantifying levels of eDNA. Consequently, the average bacterial biomass in an agricultural field was calculated as 5.95x10(9) cells/g sample, approximately 10-100 times higher than that in non- and oil-polluted fields.