.epsilon.-caprolactam is prepared by gas phase catalytic synthesis where cyclohexanone oxime is brought into contact with a crystalline zeolite, for example, aluminosilicate zeolite or metallosilicate zeolite having a constraint index of 1-12 which has been surface treated with an organometallic compound represented by the general formula: R.sub.4-n MX.sub.n wherein R which may be identical or different represent an alkyl group of 1-6 carbon atoms or phenyl group, M represnets Si or Ge, X represents Cl or an alkoxy group of 1-6 carbon atoms and n represents 1 or 2.