Long-term measurement of behaviors in experimental animals are essential to evaluate the effect of chronic drug treatment and gene mutations. Locomotor activity is one of the most important factors for the assessment of animal condition such as the circadian rhythm and motor activity. In the present study, we aimed to develop a novel recording equipment to monitor life-long locomotor activity and body temperature in group-housed mice by wireless power transmission. An electric power transmission device to generate an electromagnetic field was placed below a mouse cage, and a small receiver device with built-in measurement sensor was implanted in mouse intraperitoneal space. Obtained data were continuously transferred to a computer via Wi-Fi and were analyzed by a browser application. We have enabled monitoring data for the locomotor activity and body temperature of group-housed mice for several months under stress-free condition. These data demonstrate that the new monitoring system for locomotor activity and body temperature based on wireless power transmission enables us to phenotype genetically modified animals and to assess the therapeutic and adverse effects of drug treatment.