A method for determining the permeability of a fractured zone in the subsoil, wherein at least one well is being drilled and at least said fractured zone is encountered, includes: detecting at least one value of a characteristic quantity associated with said well; retrieving from a memory a mathematical model descriptive of said characteristic quantity and dependent on at least the permeability of said fractured zone; activating a processor for: obtaining at least one calculated value of said characteristic quantity by means of said mathematical model; comparing said calculated value with said detected value; calculating a permeability value of said fractured zone as a function of said comparison; generating an output signal representative of said permeability value. Also described is an apparatus for determining the permeability of a fractured zone in the subsoil.