The in vitro digestibility of potato starch-based foods interacting with milk protein and soybean oil was investigated. Microstructures and rheological changes upon digestion were determined. The results showed that the addition of milk proteins (casein and whey protein) promoted gelatinized potato starch digestion, while soybean oil slowed down gelatinized potato starch digestion. A mixture of soybean oil and milk protein promoted the digestion of milk protein, while a mixture of gelatinized potato starch and milk protein inhibited the digestion of milk protein. The mixture of milk protein and/or gelatinized potato starch with soybean oil promoted the release of free fatty acids in soybean oil. The highest release rate of free fatty acids was attained by a mix of milk protein and soybean oil. The mixed samples were digested and observed with a confocal laser scanning microscope. The viscosity of the digestates was determined by a rheometer. Overall, the results demonstrated that the addition of milk protein and soybean oil had an effect on the in vitro digestibility of gelatinized potato starch and its microstructure.