The molecular structure of 2-butanimine (C(4)H-3-C(3)H-2-C(2)(-C(5)H-3)=N(1)H) was determined by means of gas electron diffraction. The sample of 2-butanimine, an unstable imine, was prepared by vacuum gas-solid reaction of N,N-dichloro-2-butanamine ((C2H5)(CH3)CH-NCl2) and KOH in a glass column. The column temperature and sample pressure were optimized by measuring FTIR spectra of the reaction products in a separate experiment. The results of MP2 and DFT calculations were used as supporting information. The coexistence of the ((E)-sp and (E)-ac conformers was assumed. The structural parameters (r(g) and angle (alpha)) obtained for the (E)-sp conformer are as follows: r(C=N) 1.285(3) Angstrom; [r(C-C)] = 1.514(2) Angstrom; [r(C-H)] = 1.113(3) Angstrom; r(N-H)=1.046 Angstrom (dependent); angleN=C-C(3)=115.8(5)degrees; angleN=C-C(5)=125.0(5)degrees; angleC-C-C(4)=115.2(12)degrees; angleC-C(4)-H=113.5(14)degrees; angleC=N-H=109.3 (assumed). Angle brackets denote averaged values, and parenthesized Values are the estimated limits of error (3 sigma) referring to the last significant digit. The dihedral angle, phi NCCC, of the (E)-ac conformer was assumed to be 117.6 degrees. The abundance of the (E)sp conformer was determined to be 60 +/- 10% at room temperature