A wireless medical telemeter, which can remotely monitor a patient's biological information, has been utilized by 80.1% of hospitals in Japan. However, there are some problems such as poor reception conditions, and thus appropriate solutions are needed. In this study, we investigated the electromagnetic interference on a medical telemeter due to the surrounding structures such as walls in a hospital. The measured electromagnetic field in the building with a mesh showed , that the radio waves were attenuated by up to 13% due to the radio wave reflections by the surrounding walls.