The rotational spectrum of limona ketone (4-acetyl-1-methyl-1-cyclohexene), a key oxidation product of limonene, was recorded in the gas phase using a Fourier transform microwave spectrometer coupled to a supersonic jet expansion over the 4-20 GHz range. To display a complete view of the conformational landscape of this relatively flexible system, the relative stability and inter-conversion barriers between conformers were explored by electronic structure calculations. The lowest energy equatorial conformer was detected, and its spectroscopic molecular parameters were determined from the analysis of the spectrum. The internal rotation of the methyl group attached to the aldehyde moiety was taken into account in the analysis. The internal dynamics of the methyl group within the acetyl moiety was quantitavely described. Experimental lines of both A and E symmetry were fitted to experimental accuracy, and the experimental barrier height of the methyl group internal rotation is discussed with the support of quantum chemical calculations.