Phage-modified konpeito-like gold nanoparticles have been prepared by self-assembling phage on the surface of gold nanoparticles accumulated on glass beads. The konpeito-like gold nanoparticles were mixed with various bacteria and observed using a dark-field microscope. The bacteria were easily detected by the strong scattered light emitted by the konpeito-like gold nanoparticles bound to the bacteria (detection limit (LOD) 10000 cfu/ml). The gold nanoparticles do not bind to any host other than the host of the phage loaded on the surface of the particles, and the selectivity of the gold nanoparticles reaches not only the genus but also the species level. This method has the potential to control the bacterial selectivity of gold nanoparticles by changing the phage used, and is expected to be applied to the rapid and highly selective detection of bacteria.