To disclose a use of low branched olefin.

The synthetic base oil composition comprises a dialkyl aromatic compound having alkyl side chains of C10 to C28, or preferably alkyl side chains of C11 to C24, or more preferably alkyl side chains of C12 to C18 wherein the characteristic of branching of the alkyl side chain is more than 2.1 to less than 3.5, or preferably 2.15 to 3.25, or more preferably 2.2 to 3.0, which are the total methyl numbers (TMN) determined by the C13 NMR spectroscopy, or has more than 0.1 to less than 1.5 or preferably 0.15 to 1.25, or more preferably 0.2 to 1.0 of the branch index (BI). This synthetic base oil composition has high viscosity index, low volatility, excellent low temperature properties, and improved heat/oxidation stability and can suitably be used as a main raw material of synthetic base oil of high quality, the second base oil component or the use as a lubricant or as an additive for additive package.