The next generation (5G) mobile communication system has been the focus of studies recently. One of the approaches to enable this system is utilizing the high-SHF band (over 6 GHz) and the EHF band (mainly 30–100 GHz). To design radio links with high accuracy and evaluate 5G system performances for various scenarios, channel characteristics must be clarified. In this paper, we clarify the channel characteristics of Outdoor-to-Indoor (O2I) propagation scenario at 20 GHz band based on the measurement using a channel sounder with a 50 MHz bandwidth. The propagation mechanism is also analyzed based on estimating single scattering positions of multipath.