A roll-to-roll printing system includes driven rolls to apply a feeding force to a flexible substrate so that the flexible substrate is fed from an unwinder to a rewinder, nip rolls respectively disposed above two opposite end portions of each of the driven rolls to pressurize two opposite side portions of the flexible substrate, nip roll driving motors connected to the nip rolls to rotate the nip rolls, and a control unit to receive information regarding change of torque values of the nip roll driving motors and control tension of the flexible substrate based on the information.