Abstract: With the average molecular weight of proanthocyanidins as index,acetic acid as hydrolysis medium,the hydrolysis technology of high ploymeric proanthocyanidins （PPC）isolated by purification technology was optimized and studied. The results indicated that at 80 ℃,the average molecular weight of purified PPC extracted from grape seeds,which were hydrolyzed with 50 % acetic acid for 30 min,was decreased from 1 831.60 to 1 108.80 and the decrement was 722.8 units.