Biotinylated magnetic nanoparticles were constructed by displaying biotin acceptor peptide (BAP) on the surfaces of bacterial magnetic particles (BacMPs) synthesized by Magnetospirillum niagneticum AMB-1. Both BAP and green fluorescent protein (GFP) were fused to Mmsl3 that was isolated from BacMP membranes. The localization of the fusion protein, BAP-Mmsl3-GFP, was confirmed by fluorescence analysis. BacMPs that expressed B AP-Mms 13-GFP (BAP/GFP-BacMPs) were extracted from bacterial cells and incubated with biotin and Escherichia coli biotin ligase. The in vitro biotinylation of BAP/GFP-BacMPs was confirmed using alkaline phosphatase (ALP)-labeled streptavidin. The conjugation system developed in this study provides a method for producing biotin- or streptavidin-labeled magnetic nanoparticles without the use of a crosslinker reagent. Various functional materials can be immobilized site-selectively onto these uniquely designed BacMPs. By combining this site-selective biotinylation technology and protein display methodology, increasingly innovative and attractive magnetic nano-materials can be constructed.