Infant formulas (IFs) are the key nutritional source for infants who cannot be breastfed. There is currently a growing interest in these sensitive products in order to control their quality and to design their composition with regard to nutritional balance. In a context of sustainable development and increasing growth of the world population, it seems essential to search for alternative to animal protein in food today. Plant proteins offer interesting nutritional and functional benefits thanks to the latest improvement through research and development. In this context, five model IFs were developed with identical composition, except that 50% of the proteins were either whey proteins in the “milk-reference IF”, pea, faba bean, rice or potato proteins in the four “plant IFs” tested. The IFs were evaluated using an in vitro static gastro-intestinal model simulating infant conditions. The protein hydrolysis degree (DH) and the amino acid bioaccessibility (AAB) were used as indicators of protein digestibility. Results showed that both DH and AAB were very similar between the milk-reference IF, pea and faba bean IFs, but significantly lower for the rice and potato IFs. This study provides new insights into the impact of protein sources on IF digestibility.