The Raman and infrared spectra of niacin were measured experimentally. The molecular equilibrium geometries, vibrational frequencies, Raman and infrared intensity of niacin were calculated using the B3LYP level and cc-PVDZ basis set. Normal mode analysis was carried out using the program GAR2PED and the assignment of fundamental vibrations for niacin was obtained according to the potential energy distributions (PED). This study provides us with more quantitative vibrational spectral information which was not mentioned in previous literatures.