Noble metal-coated polydiacetylene (PDA) nanocrystals are expected to enlarge effective third-order nonlinear optical susceptibility, owing to the enhancement of optical electric field induced by localized surface plasmon. The surface of PDA nanocrystals was decorated with silver nanoparticles, and the linear optical properties were investigated. The well-defined PDA nanocrystals were first prepared by the conventional reprecipitation method as an aqueous dispersion. The following two-steps of reduction methods, namely, seed deposition and seed growth, enabled higher silver coverage on the surface of PDA nanocrystals. Silver fine seeds were successfully deposited on the PDA surface by particularly employing an anionic surfactant as a binder. The extinction spectra of the PDA nanocrystals covered with silver exhibited the red-shift and broadening of surface plasmonic peak for silver nanoparticles, which would indicate the interaction among silver nanoparticles on the same PDA nanocrystal. In addition, the red-shift of excitonic peak for PDA nanocrystals was observed, resulting from the changes of dielectric properties around PDA nanocrystal. Both spectral changes would have an influence on nonlinear optical properties of PDA nanocrystal.