The binding energy and the spherically averaged momentum distributions of orbital 1a″for butanone have been investigated by high resolution electron momentum spectroscopy (ΔE=1.15eV, Δp=0.1a.u.). The impact energy was 1200eV plus binding energy (i.e. 1206—1242eV) and symmetric non-coplanar kinematics was employed. The experimental binding energy spectra have been compared with published photoelectron spectra. The momentum profile of 1a″ orbital has been compared on a quantitative basis with theoretical calculations using Hartree-Fock method and Density Functional Theory. The position density and momentum density for 1a″ orbital are presented.