Activity of 20 wt.% MO2/S catalysts, where M = Mn, Ce and Th, and S = Al2O3 or SiO2, has been studied in cycloketonization of diethyl hexanodiate at the temperature range 573-698 K in a flow system. Only moderate yields of cyclopentanone (<35%) were achieved. The highest yields of ketone were obtained over MnO2/Al2O3 and MnO2/SiO2 catalysts - 33 and 27%, respectively. ThO2 containing catalysts were the most active, whereby ester transformations were detected below 573 K. In the presence of all catalysts the formation of the main product was accompanied by various amounts of 2-ethylcyclopentanone, cyclopent-2-en-1-one, cyclopentene, 2-cyclopentylidenecyclopentanone and numerous unidentified by-products.