This invention relates to lubricant base oil having high viscosity indexes and low pour points, and particularly to lubricant base oil consisting essentially of a normal paraffin and an isoparaffin, wherein (a) an average carbon number Nc in one molecule is not less than 28 but not more than 40, and (b) an average branch number Nb in one molecule calculated from a ratio of CH3 carbon to total carbon determined by 13C-NMR analysis and the average carbon number Nc in one molecule is not more than (0.2Nc−3.1) but not less than 1.5.