Selenium nanoparticles paved its way into the field of medicine because of its lowered toxicity and excellent biological properties. Interaction between these nanoparticles and serum proteins leads to the formation of protein corona (hard and soft) on the nanoparticle surface modulating its biological behaviour and fate. In the present study, we have emphasized on the biocorona formation of most abundant serum proteins i.e. human serum albumin, immunoglobulin-G, and transferrin on functionalized selenium nanoparticles (CTAB, SDS, and brij-58). Changes in protein adsorption pattern, mean hydrodynamic size, and zeta potential of differently functionalized selenium nanoparticles, following protein coronation were analysed for various incubation periods. Quantification of hard corona and soft corona for individual protein and for protein mixture was also done. The biological impact of protein coronation on selenium nanoparticles was evaluated by the cellular uptake and cell viability studies. Finally, modulation in radical scavenging property of selenium nanoparticles before and after protein corona formation was studied through DPPH assay.