Abstract: The electronic structure of five conformers of 2-chloroethanol was studied by ab initio cal-culations at B3LYP and MP2 levels of theory with aug-cc-pVTZ basis set. The existing hydrogen bond and hyperconjugation effects on the stability of 2-chloroethanol conformers were discussed on the base of natural bond orbital analyses. The result exhibits that hyper-conjugation is the main factor to determine the stability of conformers. Such effects on the electron wavefunctions of the highest-occupied molecular orbital (HOMO) of different con-formers are demonstrated with electron momentum spectroscopy, exhibiting the obviouslydifferent symmetries of the HOMO wavefunctions in momentum space.