The jet-cooled Fourier-transform microwave spectrum of N-methylaniline (C 6 H 5 -NHCH 3 ) was recorded in the region of 10–26GHz, and was analyzed to determine rotational constants and nuclear quadrupole coupling constants. Furthermore, a Coriolis-like coupling parameter characterizing an interaction between an internal rotation of a methyl group and an overall rotation was also determined from A–E splittings observed in pure rotational transitions with high K a values. The Coriolis-like coupling parameter permitted the determination of the barrier to internal rotation of the methyl group which was found to be 975cm −1 .