In this paper, we produce porous silicon (PSi) by electrochemical etching, and it is the first time to evaluate the performance of label-free porous silicon biosensor for detection of variable domain of heavy chain of heavy-chain antibody (VHH). The binding of hen egg white lysozyme (HEWL) and VHH causes a red shift in the reflection spectrum of the biosensor. The red shift is proportional to the VHH concentration in the range from 14 g·ml⁻¹ to 30 g·ml⁻¹ with a detection limit of 0.648 ng·ml⁻¹. The research is useful for the development of label-free biosensor applied in the rapid and sensitive determination of small molecules.