The application of biochar (BC) as a soil amendment is of growing interest. BC has recently been shown to decelerate the cycling of soil organic N, and adsorption of proteins to BC surfaces has been put forward as an explanation. However, the effect of BC on the sorption of proteins in soil is largely unknown. The main objective of this study was therefore to test the sorption of a model protein (bovine serum albumin, BSA) on a soil amended with different types of BC. Contrary to our assumption, BC application reduced the sorption of BSA. The BC feedstock type and pyrolysis temperature affected BSA sorption; however, the underlying mechanisms require further investigation. BC-induced liming had no effect on BSA sorption, while BC’s hydrophobicity and surface area seemed to be important factors.