Experimental observations have confirmed that the addition of a single electron to polycyclic aromatic hydrocarbons (PAHs) can excite the plasmon resonances in visible region (Lauchner a al., 2015). To gain more information, we fulfill a fully quantum-mechanical study of tunable plasmonic behavior in acene. The absorption spectra demonstrate that the molecular plasmons are tunable by addition or removal of single electrons. However, the plasmon exhibits a sharp different tunability for electron doping and hole doping due to the asymmetry electronic structure. Furthermore, the plasmon resonances in doped acene show a nearly linear relationship between the plasmon wavelength and molecule length.