An apparatus for measuring outdoor temperature and humidity includes a box type body which has a flat LCD screen located on one side, and a temperature sensor and a humidity sensor located on the surface thereof. The body includes a control circuit. The temperature sensor and humidity sensor, a temperature and humidity measuring circuit and LCD screen are integrated in one set. The body may be mounted on the exterior of a glass window by means of a fastening section located on the body without assistance of skilled professionals. Thus installation time and costs and wiring expenses may be saved. Outdoor temperature and humidity may be directly known indoors.