The pure rotational spectrum of methoxyacetonitrile, CH3OCH2CN, has been investigated in the 8–40 GHz region. Spectra of the gauche and trans conformers, with respect to rotation about the O—CH2 bond, have been assigned. The rotational constants for the ground vibrational state are (in MHz) gauche: A = 11893.36(0.05), B = 3423.26(0.02), and C = 2871.53(0.02); trans: A = 29610(90), B = 2470.96(0.02), and C = 2348.07(0.02). The centrifugal distortion parameters DJ and DJK have also been determined for each conformer. The dipole moment components for the gauche conformer have been measured as (in D): µa = 2.40(0.03), µb = 1.37(0.10), µc = 1.11(0.11), and µ = 2.98(0.07). On the basis of relative intensity measurements at 25 °C the abundance of the trans form has been estimated as 4.8 ± 2.4% with the energy difference Etrans − Egauche having the value 5.7 ± 1.7 kJ mol−1 (1.35 ± 0.4 kcal mol−1). From vibrational satellite intensities the frequency for the first excited state of skeletal torsion about the O—CH2 bond has been found as (in cm−1) gauche: 93(25) and trans: 74(32). From the observed values of the rotational constants the dihedral angle in the gauche conformer is found to be near to 69° from the cis position.