An inkjet printing system is provided, which comprises: a stage on which a substrate including at least two alignment keys is mounted; an inkjet head device disposed above the stage; and an alignment key sensing device disposed above the stage, wherein the inkjet head device comprises a head unit including an inkjet head, and a supporting unit which supports the head unit and scanning the substrate in a first direction, and wherein the alignment key sensing device comprises: at least two alignment key sensors for sensing positions of the alignment keys; a sensor supporting unit for supporting the at least two alignment key sensors; and a sensor position adjustment device for adjusting positions of the alignment key sensors with respect to the alignment key sensing device.