There is provided a method for producing a polarizer having improved cross transmittance. The method for producing a polarizer includes: dyeing a polyvinyl alcohol (PVA)-based film with molecular iodine by immersing the PVA-based film in an aqueous iodine solution (a dyeing step); absorbing the molecular iodine into the PVA-based film using an aqueous boric acid solution (a cross-linking step); arranging the molecular iodine in the certain direction by stretching the PVA-based film in a certain direction (an stretching step); and drying, in an oven, the PVA-based film in which the molecular iodine is oriented; wherein a phosphate compound is added to the iodine aqueous solution (the dyeing step) or the aqueous boric acid solution (the stretching step) so that a weight ratio of the boric acid: the phosphate compound is in a range of 1:0.1 to 1:10.