A magnetized low‐pressure rf plasma used for thin‐film preparation has been observed with probe measurements. The sheath structure near the rf electrode was also obtained by measuring the potential profile in the sheath with an emissive probe. The results revealed that the magnetic field increases the electron density but has no effect on the electron temperature. Further the magnetic field increases the magnitude of the self‐bias potential of a rf electrode, and it decreases the effective sheath thickness. The application of a magnetic field to the conventional rf processing plasma is confirmed to be useful for control of a low‐pressure rf plasma.