Activity of pure Al2O3 has been studied in cycloketonisation of various dialkyl alkanodiates of general formula (CH2)(n)(COOR)(2), where n = 4, 5, 6, 7, 8 and 10 and R = Et, s-Bu and t-Bu at the temperature range 598-723 K in a flow system. The yields of cycloalkanones strongly depend on the size of the ring formed, the structure of alkyl group in ester molecule and on the reaction temperature. Cyclopentanone, cyclohexanone and cycloheptanone were obtained with yields 50-60% from the appropriate diethyl esters. The only low yields (<8%) of cyclooctanone, cyclononane and cycloundecanone were achieved. An increase in the order of the ester alkyl group leads in some cases to higher yields of ketones - di-t-butyl hexanodiate yielded 88% of cyclopentanone.