A 6‐Gc traveling‐wave maser has been operated in a novel transverse field superconducting magnet. The magnet produces a uniform field in excess of 4000 Oe over a volume of 1.2×1.5×6 in. The field is directed across the shortest dimension (perpendicular to the direction of propagation) which permits nonreciprocal gain and attenuation. The TWM exhibited net gain in excess of 30 dB with 3‐dB bandwidths of about 20 Mc. Gain and bandwidth characteristics were the same as those measured on the same traveling‐wave maser in the field of a large laboratory magnet. This indicates a field homogeneity of about ±1 Oe or better in the superconducting magnet over the ruby volume of the maser since greater deviations would result in decreased gain and increased bandwidth.