We theoretically study the optical properties of monolayer C3N within the framework of linear response theory by using a two band effective k⋅p Hamiltonian. We find that both the effective masses and optical conductivities are anisotropic arising from the anisotropic band structure at the M point. Although the inter-band coupling only exists in the armchair (x-)direction, the effective mass along the armchair direction is larger than that along the zigzag (y-)direction. Interestingly, the absorption part of the optical conductivity Re σxx excited by linearly polarized light along the armchair direction is an order of magnitude larger than Re σyy excited by linearly polarized light along the zigzag direction, resulting in a strong linear dichroism, because the inter-band optical conductivity is dominated by inter-band coupling which only exists in the armchair direction. Finite doping can adjust the optical conductivities i.e., Re σxx and Re σyy and modulate the linear dichroism, but the effects of n-type doping and p -type doping are different because of the electron–hole asymmetry. Our results provide further understanding of the electronic state of monolayer C3N and maybe useful to design polarized optical devices based on it.