Disclosed are monomeric avidin-like proteins with a strong and stable biotin-binding ability, protein conjugates containing two or more of the monomeric avidin-like proteins and having a multivalent binding ability to biotin, nucleic acid molecules for encoding the monomeric avidin-like proteins, and methods for producing the monomeric avidin-like proteins, so the monomeric avidin-like proteins, due to the monomeric structure, are free from a problem of the disruption of receptor functions, caused by oligomerization occurring in existing tetrameric streptavidin or tetrameric but monovalent streptavidin variants.