Under Ambient Intelligence auspice, many researchers have studied the area of context recognition such as location, users' identity and activities, and other parameters related to users' situation in the environment. One aspect of context that is pertained to the users' situation is body posture of a sitting person. The aim of this paper is the design and development of a novel Aware Chair system that recognizes sitting body postures. The Aware Chair is based on digital sensors mounted on the sitting and back area of the chair. The chair is tested using 50 people with different gender, body mass, and height. The design details of the system as well as test results are presented in this paper.