Abstract: The concentration of oligo(glycolic acid)2 (OGA-2) and its hydrolysis product glycolic acid (GA) were monitored by capillary electrophoresis with UV detection. A new mathematical model was used to build the relationship between the reaction conversion and peak areas of OGA-2 and GA, and then calculate the reaction rate constants of diglycollic acid hydrolysis in 50 mmol·L-1 phosphate buffer at varied temperatures. At 343, 353, 363 K, the measured rate constants of diglycollic acid were 4.8×10-3, 9.6×10-3, 1.85×10-2min-1, respectively. The apprarent activation energy of the hydrolysis was calculated to be 69.8 kJ·mol-1.