The catalytic activity and selectivity of a number of aluminosilicate catalysts with different degrees of crystallinity Z in the conversion of ethylene to higher hydrocarbons have been studied in a flow-type unit at atmospheric pressure in the temperature range 300-600 degrees C. The observed extremal dependence of the overall C2H4 conversion on Z is explained by the influence of macrokinetic factors on the reaction with Z > 55%. It is suggested that the initial stage in C2H4 conversion is the formation of a surface high-molecular weight ethylene oligomer. The observed range of products is the result of cracking of the adsorbed oligomer.