We have studied the molecular structure of tert-butyl acetate, C(3)H3C(=O(2))(1)O(4)C(C(6)H-3)(C(8)H-3)(5)C(7)H-3, by gas electron diffraction and HF/4-21G calculations on geometrical parameters and harmonic force constants. Experimental data are consistent with the assumptions that the C1=02 bond is cis to the O4-C5 bond and that the tert-butyl group is staggered with respect to the C1-O4 bond. The structural parameters (r(g)/Angstrom and angle(alpha)/deg) with estimated limits of error (3 sigma) are r(C1=O2) = 1.198(5), r(C1-O4) = 1.334(6), r(O4-C5) = 1.456(8), [r(C-C)] = 1.522(2), [r(C-H)] = 1.101(4), angle O2C1C3 = 120.4(24), angle O2C1O4 = 126.1(5), angle C1O4C5 = 122.3(9), angle O4C5C6 = 101.5(10), angle O4C5C7 = 110.0(8), angle C6C5C7 = 111.4 (fixed at the HF/4-21G value), and [angle CHHMe] = 108.0(10). The C6 and C7 atoms are trans and gauche to the C1-O4 bond, respectively, and [] denotes average values. The differences between structural parameters of similar types have been taken from the HF/4-21G calculations. The C1-O4 bond length in tert-butyl acetate is about 0.03 Angstrom shorter than that in methyl acetate. This shortening can be rationalized in terms of the electron-releasing inductive effect of substituents and the resonance effect. The steric effect of the tert-butyl group is seen in angle C1O4C5, angle O2C1C3, angle O2C1O4, and the tilt angle of the tert-butyl group.