The Fourier transform microwave spectra of the E and the Z isomer of butadienyl acetate were measured in the frequency range from 2 to 26.5 GHz under molecular jet conditions. The most stable conformer of each isomer, in which all heavy atoms are located in a symmetry plane, was identified after analyzing the spectrum by comparison with the results from quantum chemical calculations. The barriers to internal rotation of the acetyl methyl group are 149.1822(20) cm−1 and 150.2128(48) cm−1 for the E and the Z isomer, respectively, and are similar to that of vinyl acetate. A comparison between two theoretical approaches treating internal rotations, the rho axis method and combined axis method, is also performed. The influence of the alkyl chain R on the methyl torsional barriers in acetates CH3-COOR is discussed.