A wireless tire-pressure monitor mainly has a cylindrical body, a seal assembly, a screw and a sensor. The cylindrical body is mounted through a hole in a wheel rim wall and has an air passage, an interior thread defined in the air passage and a flange formed around the body. The seal assembly is mounted around the body on opposite sides of the wheel rim wall and abuts the flange on the body. The screw is screwed into the air passage and squeezes the seal assembly against the wheel rim wall. The sensor is mounted on the body. Therefore, the wireless tire-pressure monitor is easily and securely attached to the wheel rim to detect pressure and temperature of the wheel. Further, the sensor is positioned outside of the wheel rim to prevent the wireless detecting signals from being interfered by the wheel rim or wheel.