The present invention provides a surface acoustic wave sensor capable of suitably controlling the flow of a liquid sample onto IDT electrodes. A surface acoustic wave sensor has a piezoelectric substrate, a first IDT electrode and a second IDT electrode which are located on the upper surface of the piezoelectric substrate and are separated from each other while sandwiching a detection part on the piezoelectric substrate therebetween, and the cover which forms the space being on the first IDT electrode, second IDT electrode, and the detection part and straddling them. On the lower surface of the cover, the detection part-facing surface facing the detection part has a smaller contact angle to the liquid sample than that of a pair of electrode-facing surfaces facing the first IDT electrode and second IDT electrode.