A wireless radiation monitoring system has been developed using a sensor network and one board-type radiation module. The one board-type radiation module is based on the Pocket Geiger type5 by Radiation-watch.org. The power consumption of the module was reduced to 3 mW to drive the monitoring system by a solar cell. The module is designed to connect a Gvove terminal of Arduino microprocessors. The radiation dose rate was transmitted by wireless modules (Xbee, RF bee, etc.), and collected by the application program. The communication distance of the module was around 40-160 m in a straight-line distance. A novel 920MHz module has been developed by combining the radiation module and a PIC32bit microprocessor. The communication distance by using the module is over 3 km in a straight-line. Software was designed to form a mesh network. Because a lower power radiation detector is required for environmental measurements around the Fukushima nuclear plant, a custom detection ASIC has been designed using a 0.6-μm CMOS process. The power consumption of the circuit was 1.5 mW.