Abstract: In this work, we synthesized monodispersed hexagonal Ag nanoprisms in high yields in a system of poly(vinylpyrrolidone) (PVP) in N-methylpyrrolidone (NMP). A blue shift occurred and was strongly dependent on the thickness of the uniform Ag nanoprisms, which had almost the same radial area. When the Ag nanoprisms grew thicker, their in-plane dipole resonance peaks markedly shifted toward shorter wavelengths (i.e., blue shift). PVP played a critical role of favoring vertical growth of the Ag nanoplates, preventing aggregation, and inducing the formation of Ag hexagonal nanoprisms (HNPs) through the transformation from thin Ag triangular nanoprisms (TNPs). Compared with similar previous research, the present study provides quite uniform Ag hexagonal nanoplates, which makes the blue shift related more solely and distinctly to the thickness of the Ag nanoprisms. The findings of this work provide a new perspective toward understanding the unique optical characteristics of Ag HNPs with different aspect ratios.