Rotational transitions were measured for the methanolrtrimethylamine (methanolrTMA) complex and four of its isotopomers, using Fourier transform microwave spectroscopy. A partial analysis of the spectrum revealed that both the TMA subunit and the methyl group in methanol undergo hindered internal rotations. The rotational transitions associated with the ground torsional state of TMA and the two lowest A and E states of methanol were assigned and fit. A simplified two-top torsion-rotation Hamiltonian was used in the analysis. From the fitted parameters, a nearly linear hydrogen-bonded structure was obtained for the complex. The NrrrH distance was determined as 1.92 A ˚. The TMA symmetry axis was found to be tilted 5.5Њ from the NrrrH hydrogen bond. The apparent methyl group torsional barrier height (in methanol) was determined to be 174 { 10 cm 01 , from which the OH bending potential barrier height was estimated to be 1178 { 200 cm 01 . The potential barrier that hinders the TMA internal rotation was estimated as 32 { 5 cm 01 . The dipole moment of the complex was m T Å 2.87 { 0.15 D. Comparison of the hydrogen bond strength of this complex with some related methanol complexes was made using hydrogen bond lengths and the apparent methyl torsional barrier heights.