Ubiquitous sensor networks are application oriented system, which are composed of a large number of cooperative sensor nodes. The identification of individual sensor node is important especially for some security-sensitive applications. In this paper, we focus on the establishment of trust relationship among wireless sensor nodes, and try to combine the message authentication and identity authentication as a countermeasure to hostile attack. Accompanied with a simple lightweight key pre-distribution algorithm, in which each node sends only one message, we propose a lightweight trust relationship establishing scheme for ubiquitous sensor networks. The new scheme, which works without a trusted authority in the network, is not only concise in format but effective in practice to ensure network trusted and secure.