A study has been made of the conversion of piperylene on oxide catalysts based on group II metal oxides containing Fe2O3. It has been found that, on these catalysts at 630 degrees C, piperylene forms cyclopentene, cyclopentadiene, 1,4-pentadiene, cracking products and products of hydrogen transfer (n-pentenes). The highest yield of C-5 cyclic hydrocarbons is achieved by Fe2O3-MgO (11%). Cyclizing activity is also exhibited by individual oxides, and here the yield of cyclic hydrocarbons increases with increasing basicity of the oxide, while the 1,4-pentadiene yield increases in reverse order. The highest 1,4-pentadiene yield is observed on BeO and its compounds with magnesium oxide. The highest yields and selectivity (6 and 77% respectively) were obtained on a catalyst containing 80% BeO and 20% MgO at a temperature of 575 degrees C with a volume feed rate of piperylene of 1.0 h(-1) and a steam dilution molar ratio of 1:10. The yield obtained amounts to two thirds of the thermodynamically possible yield.