We show that the microstructures of polycrystalline ice can serve as a confining template for one-dimensional assembly of colloidal nanoparticles. Upon simply freezing an aqueous colloid, the nanoparticles are excluded from ice grains and form chains in the ice veins. The nanoparticle chains are transferable and can be strengthened by polymer encapsulation. After coating with polyaniline shells, simple sedimentation is used to remove large aggregates, enriching single-line chains of 40 nm gold nanoparticles with a total length of several micrometers. When gold nanorods were used, they formed one-dimensional aggregates with specific end-to-end conformation, indicating the confining effects of the nanoscale ice veins at the final stage of freezing. The unbranched and ultralong plasmonic chains are of importance for future study of plasmonic coupling and development of plasmonic waveguides.