The microwave spectrum of ethanimine, CH3CH=NH, has been measured over the range of 18-76 GHz. A series of lines have been attributed to the Z-isomer. These have been fitted to an asymmetric rotor with inclusion of centrifugal distortion parameters. An excited torsional state has also been assigned and the barrier to internal rotation of the methyl group has been determined. The dipole moment has been evaluated from the Stark effect as 2.42 D. The quadrupole coupling constants of the nitrogen atom have been obtained from high-resolution studies. In contrast to methanimine, we found no evidence of magnetic hyperfine interaction in the structures of the multiplets.