Weather radar acquires conditions of weather, such as amount of rainfall and snowfall in the air. The observed data from weather radar are widely applicable for weather forecasts, weather alert and various other fields. Waveguide rotary joints allow the directional antenna to rotate while passing microwave signals to and from the transceiver. The rotary joints installed on the weather radar are required steady characteristics and long life operation. Since JRC has developed the waveguide rotary joints with high reliability that incorporated both mechanical components selection and optimized transmission characteristics specialized for weather radar, we introduce about this device in this paper.