In order to improve soy yogurt products, the effect and underlying mechanism of different types of milk proteins, whey protein isolate (WPI), milk protein concentrate (MPC), and sodium caseinate (NaCas), on the gelation behavior of soymilk were investigated. The results showed that the incorporation of WPI (≥ 20%) or 40% NaCas could effectively enhance the strength of soymilk gels, and WPI (≥ 20%) had the most positive effect. Low levels of replacement of milk proteins could significantly decrease the particle size of soymilk gels, while high proportions of WPI replacement had the opposite effect. In term of microstructure, MPC led to more organized and denser networks. NaCas induced the formation of filamentous networks. WPI induced the formation of a less organized but denser gel structure. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that WPI (≤ 20%) might promote the involvement of the β subunit of soybean 7S protein in gel formation, while NaCas might hinder the gelation of the basic subunit of soybean 11S protein.