Abstract: The combined modification (phthalation followed esterification) of gelatin and the effect of esterification on the isoelectric point of phthalated gelatin were studied. The experimental results showed. 1. The isoeleetric point of the parent alkali-processed gelatin is 4.57. 2. After the carboxy groups of gelatin were esterified with ethanol, the isoeleetric point of esterified gelatin may be raised up to 5.78 even to 9.60 depending on the degree of esterification. 3. The isoeleetric point of esterified and then phthalated gelatin (PEA gelatin) was 0.48 pH unit higher than that of phthalated gelatin (PA gelatin). 4. The coagulating property of PA and PEA gelatin differs greatly.