Disclosed is a substrate processing system including a nozzle to supply a chemical solution containing a mixture of first and second solutions onto a substrate loaded on a supporter of a process chamber, a chemical solution supplying system to supply the chemical solution to the nozzle, and a controller to control the chemical solution supplying system. The chemical solution supplying system may include a mixing tank mixing a plurality of chemicals to produce the first solution, a supply tank receiving the first solution from the mixing tank and producing the chemical solution, a connection line to connect the mixing tank to the supply tank, and a valve and a pump on the connection line. The pump is controlled to allow the first solution to be supplied into the supply tank at a predetermined supply amount per stroke.