Di-galacturonic acid (Di-GalA) and tri-galacturonic acid (tri-GalA) are emerging as new prebiotics. A novel biorefining strategy was established to prepare di-GalA and tri-GalA (oligogalacturonic acids) from commercial pectin, which utilized a two-stage process consisting of a hydrothermal pretreatment of low-esterification pectin (LP) followed by enzymatic hydrolysis with endo-polygalacturonase. Hydrothermal pretreatment at 140 degrees C for 35 min significantly decreased molecular weight, esterification degree and viscosity of LP. The pretreatment process was found to greatly enhance subsequent enzymatic hydrolysis by increasing the accessibility of substrate to enzyme and weakening the steric hindrance effect of enzymatic hydrolysis. The oligogalacturonic acids yield of 75.3 % and 84.8 % of the selectivity of endo-polygalacturonase to oligogalacturonic acids after enzymatic hydrolysis of hydrothermal pretreated LP at enzyme loading of 10 U/g pectin for 24 h were obtained.