Abstract: The effect of whey protein and its hydrolysates on the in vitro digestibility and physicochemical properties of potato starch (PS) was investigated by constructing the co-gelatinization system between the PS and whey protein or whey protein hydrolysates. The results showed that whey protein hydrolysates hydrolyzed by pepsin-pancreatin (WPP) had the best inhibitory effect on the digestibility of starch. Thereinto, the native PS displayed the highest rapidly digestible starch (RDS) content (94.54%) and lowest resistant starch (RS) content (3.10%). Lower RDS (67.51%) and higher RS (12.69%) contents were found for PS-WPP120 complex. The inhibitory effect of whey protein hydrolysates on the swelling and gelatinization of PS was stronger than that of whey protein. Therefore, the molecular weight of whey protein hydrolysates had a notable influence on both physicochemical properties and in vitro digestibility. And whey protein or its hydrolysates strengthened the hydrogen bonding and increased the order degree of PS structure, indicating that the interactions between PS and whey protein or whey protein hydrolysates could reduce in vitro digestibility of PS.