Abstract The catalytic liquid phase hydrogenation and/or isomerization of cyclohexene are investigated at 160–350°C under 50–90 kg/cm2 of hydrogen or atmospheric nitrogen using molybdenum trisulfide and various other metal sulfides or oxides, with or without additives, as catalysts. The activity of catalysts is found to be in the order of MoS3≥MoS2>WS3>CoS3>NiS2. The hydrogenation product is almost entirely cyclohexane, except when molybdenum trisulfide is used as a catalyst, in which case the reaction at 310°C accompanies isomerization to a considerable extent, yielding up to 24% of methylcyclopentane. The molybdenum disulfide catalyst with the addition of sulfur or hydrogen sulfide is similar to the molybdenum trisulfide in its selectivity for the course of reaction. The reason for these results is discussed. The main isomerization reaction path is found to be cyclohexene → methylcyclopentene-(1) → methylcyclopentane.