We aim to study the structure of nanoparticle (NP) monolayers formed thanks to the interaction between negatively charged silica NPs and bovine serum albumin (BSA). In particular, we will investigate how the dispersion composition (NP/BSA ratio and ionic strength) will affect the monolayer structure and density by means of grazing incidence small angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR). Then, the monolayers will undergo a compression/expansion cycle in a Langmuir trough and, during both compression and expansion, GISAXS and XRR will be performed. This will allow determining the inter-particle distance variation and eventual desorption/re-adsorption phenomena. This study will provide new fundamental insight on the effect of NP/BSA interactions on the conformation of adsorbed BSA. Moreover, it will allow assessing the use of mixed NP/BSA dispersions as novel green adaptive surfactants for the stabilization of complex fluid interfaces.