There is proposed a washing solution for washing an inkjet printer head which performs printing by feeding an ink comprising at least two kinds of polymerizable compounds each differing in viscosity, a photopolymerization initiator, and pigment. This washing solution is characterized in that it contains not less than 50 parts by weight of a polymerizable compound selected from the polymerizable compounds included in the ink and having a lowest viscosity among the polymerizable compounds, or not less than 50 parts by weight of a polymerizable compound having a viscosity of 30 mPasec or less at ordinary temperature.