Disclosed are a new dichroic dye having liquid crystal properties and dichroic properties and capable of being used for forming a polarization film with excellent heat resistance, durability, and polarizing properties, a composition including the same for a polarization film, a method for forming a polarization plate with excellent durability using the composition, and a polarization plate prepared thereby. The new dichroic dye has a structure of R1-L1-(M,L,D) (where, D is a dichroic structure, M is a structure with liquid crystal properties, R1 is a reactive end functional group, and L and L1 are linking structures). The composition for a polarization film includes the dichroic dye. In the method for forming the polarization plate, the composition for a polarization film is applied to a substrate and cured to prepare the polarization plate. The polarization plate has excellent dichroic ratio, heat resistance, durability, and polarizing properties.