The stability of a special three‐dimensional shearing boundary layer with imbedded shearing magnetic fields is studied. Boundary layer solutions are obtained for a finitely, electrically conducting fluid, and then the sixth‐order differential equations describing the instability are solved numerically. It is found that the flow is always unstable and that the neutral stability curves pass through the origin of the&agr;‐Rdiagram, where&agr;is the wave number andRis the Reynolds number. An increase of the magnetic field tends to stabilize the flow when the conductivity is small or extremely large. An increase of resistivity has a stabilizing effect at moderate magnetic Prandtl number and a destabilizing effect at high magnetic Prandtl number.