To provide a urea water injection valve for solving the problem of the deterioration in NOx reduction ratio and an ammonia slip caused by an ammonia supply shortage by promoting the atomization of urea water.

This urea water injection valve is provided for injecting the urea water into an exhaust passage of an internal combustion engine, and has a nozzle holder 24 forming a plurality of nozzle ports 28a for injecting the urea water on a concentric circle and internally forming a urea water passage 27 communicating with the nozzle ports 28a, a body member composed of a nozzle body 25 and a nozzle port plate 28, and a needle 26 for opening and closing the urea water passage 27 by being seated on and left from an annular ring-shaped seat 25a formed in the nozzle body 25. The ratio Ds/Dp of a seat diameter Ds being a diameter of the seat 25a to a pitch diameter Dp being a diameter of the concentric circle of the nozzle ports 28a is set to 1.3Ds/Dp2.5.