With the progress of wireless networks, sensor networks, RF-ID networks, etc. ubiquitous environment providing context-aware service to users everywhere becomes possible, so that our living and working environment becomes more convenient. On the other hand, the more devices the environment employs, the more danger it is, if the system/services go out of order. Therefore to guarantee safety becomes an important problem in ubiquitous environment. Functional safety is a concept regarding safety, which means even though the device has some problems or failures, the system should have some ways to guarantee people/equipment get less damages than a designed level. Concepts and methods of functional safety have been used in many traditional industries, such as nuclear energy industry, railway, etc. for years, but have not been well used in ubiquitous systems. In this paper, we compare the difference of ubiquitous system with the systems used in traditional industries. Then we pose some problems which should be solved for the functional safety in ubiquitous environment and discuss some ideas for solving the problems. We also show an example considering the functional safety in design of a ubiquitous application.