ABSTRACT Investigated is the relation between the hydrofracturing pressure Pf and the strength of cohesive soils. Fracture tests on six kinds of cohesive soils (i. e. ϕ = 0 materials), including artificial soils, were performed. The direction of fracture surface was chosen not only vertical (i. e. parallel to the borehole) but also horizontal and inclined. The result is the following equation in terms of total stress. Pf = σmin + qu σmin: the minimum principal stress, qu: the unconfined compression strength The shear failure—rather than the tensile failure—near the borehole initiates the hydrofracture of cohesive soils. This fracture mechanism seems to be reasonable, especially in case of the horizontal or inclined fracture. The viscosity of liquid in the borehole, the sample size and the pre-existent crack around the borehole have little influence on the fracturing pressure as far as the pressurizing rate is high enough to prevent the liquid to penetrate into the wedge.