The purpose of this paper is to suggest guidelines for application on USN (Ubiquitous Sensor Network) based on the field study. USN detects, stores, processes and integrates the object and environment data via tags and sensors then generates the situation aware information and knowledge contents to allow anyone to freely use the customized knowledge services anywhere and anytime. Forthcoming ubiquitous society can be embodied early by building USN infrastructure, and the USN technologies create a positive ripple effect on related industries by rapid added values of the cutting-edge of IT services and products that improve the quality of citizens' life styles. Even through USN technology developments are lively in progress, their practical studies are in sluggish. For these reasons, National Information Society Agency (NIA) carried out four different field studies such as u-Marine, u-Architecture, u-Agriculture, and u-Hospital in order to examine USN feasibility in 2005.