Catalytic epoxidation of cycloalkenes to corresponding epoxides using molecular oxygen was carried out in presence of cobalt(II) exchanged zeolite X based catalysts. Effect of temperature (353-418 K) and pressure (30-150 psi) was studied to obtain the optimum conditions for the reaction. The best results were obtained at 60 psi pressure and 373 K using NaCoX96 catalyst with cycloalkene conversion and epoxide selectivity for cyclohexene, cycloheptene and cis-cyclooctene were obtained in the range 26-47 and 48-100% respectively. Alkali and alkaline earth cationic promoters were introduced into the zeolite catalyst in order to study the effect of basicity of the catalyst on the cycloalkene conversion and epoxide selectivity. Cobalt(II) exchanged zeolites X, NaCoX96, seems to be efficient heterogeneous catalysts for the epoxidation reactions using molecular oxygen. The catalyst was observed to be recyclable as conversion and selectivity were retained even after four catalytic reaction cycles. (c) 2007 Elsevier B.V. All rights reserved.