The naphthenic base oil has been formulated to insulating and refrigerating oils. In the views of decreasing of the naphthenic crtide oil, new sources as its replacement have been needed. To solve this situation, the synthesis of naphthenic oil has been carried under hydrogenation reactions of alkyl aromatic compounds using various catalysts. The sturcture of reaction products has been investigated using spectroscopic methods such as NMR, UV, IR and HPLC. On the basis of the experimental results, it was convinced that unsaturated aromatic ring was saturated to saturated rings, and also optimum cond~tions established. Throughout this study, new resource as the replacement of conventional naphthenic oil has introduced.