A microscope objective having at least four lenses or groups of lenses and which can be used to improve image contrast. According to the invention, a phase plate, aligned concentrically to the optical axis, can be integrated into and taken out of the air space between the first lens and the second lens, as viewed from the object side. The defined arrangement of the phase plate and the associated shift of the real pupil into the air space between the first two lenses or groups of lenses, respectively, of the microscope objective allows a microscope objective, initially designed as a bright-field variant, to be redesigned as a phase contrast variant with relative ease.