The dependence of activity and selectivity of a nickel sulfate catalyst for propylene oligomerization on the temperature of its preliminary calcination was studied. It was found that, in order to achieve active operation, it was necessary to preliminarily activate the catalyst by calcining at a high temperature in a nonreducing atmosphere (air or nitrogen). The optimal temperature range of activation is 400-600degreesC (preferably 500degreesC). The nickel sulfate catalyst treated under these conditions ensures not only high propylene conversion into oligomers but also the selectivity for dimers.