PEG immunogenicity and its accelerated blood clearance for certain PEG-modified nanoparticles and drug delivery carriers. Zwitterionic nanoparticles have drawn significant attention in recent years for their excellent non-fouling properties and potential in applications due to their long circulation half-life and low immune response. In this work, we investigate the composition of in-vivo protein corona formed on zwitterionic nanogels to understand the mechanism of evading phagocytosis of zwitterionic nanoparticles in vivo. PEG nanogel was used as a control. Results show that zwitterionic polymers not only reduce protein adsorption but also influence the composition of protein corona on nanoparticles. The preferential albumin adsorption and the trace amount of total adsorbed proteins on zwitterionic nanogels help to elucidate how these nanogels prevent non-specific cellular uptake and prolong blood circulation time.