Physically crosslinked hydrogels based on gelatin functionalized with desaminotyrosine (DAT) (giving Gel-DAT) or desaminotyrosyl tyrosine (DATT) (resulting in Gel-DATT) have shown high potential as biomaterials. Here, protein adsorption to the functionalized gelatins in comparison to gelatin was quantified to see if the functionalization and chain organization of gelatins has an influence on the amount of proteins being adsorbed. For this purpose, gelatin, Gel-DAT, and Gel-DATT were incubated with water or aq. solutions of bovine serum albumin (BSA), fibrinogen, or fibronectin, respectively, at physiological concentrations. Protein concentrations in the supernatant were determined with the bicinchoninic acid (BCA) assay before and after the contact. BSA adsorption to the materials was influenced as well by the hydrophobicity of the material as the degree of swelling, with the observation that higher protein concentrations led to lower protein adsorption. The highest amount of fibronectin was adsorbed to Gel-DAT, followed by gelatin and Gel-DATT, with only small differences for different initial protein concentrations. Fibrinogen adsorption increased with increasing concentration. In the future, adsorption studies based on specific antibody-based techniques might enable quantification of the proteins also in competition assays and direct quantification of adsorbed material.