Abstract: Polyacrylonitrile (PAN) ultrafiltration membrane modified with hyperbranched polymer polyamide-amine (PAMAM) was investigated in detail. First, PAN membrane was treated with the alkali solution to produce carboxyl groups on its surface. Then, PAMAM solution was used to react with the hydrolyzed PAN membrane at different temperatures to prepare PAN-PAMAM membranes. The obtained membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy(AFM). FT-IR spectra and XPS results proved that PAMAM molecules were immobilized onto the surface of PAN-PAMAM membrane by the condensation reaction between -COOH groups of hydrolyzed PAN and -NH₂ groups of PAMAM. SEM images revealed that a new dense and smooth layer was formed on the surface of PAN-PAMAM membrane, which was composed of PAMAM. Moreover, both the morphology and the thickness of the layer changed with the reaction temperature. AFM images further revealed that the surface roughness of the membrane decreased obviously after modification. For PAN-PAMAM membrane prepared at 80℃, the water contact angle declined by 20° compared with the original PAN membrane. PAN-PAMAM membrane showed a decreased water flux and an increased retention rate after modification. PAN-PAMAM membrane showed a water flux of 14.9 L/(m²·h), and its retention rate of PEG2000 reached 91.4%.