Measurement of human motion is widely required for various applications, and a significant part of this task is to identify motion in the process of human motion recognition. There are several application purposes of doing this research such as in surveillance, entertainment, medical treatment and traffic applications as user interfaces that require the recognition of different parts of human body to identify an action or a motion. The most challenging task in human motion recognition is to achieve the ability and reliability of a motion capture system for tracking and recognizing dynamic movements, because human body structure has many degrees of freedom. Many attempts for recognizing body actions have been reported so far, in which gestural motions have to be measured by some sensors first, and the obtained data are processed in a computer. This paper introduces the 3D motion analysis of human upper body using an optical motion capture system for the purpose of gesture recognition. In this study, the image processing technique to track optical markers attached at feature points of human body is introduced for constructing a human upper body model and estimating its three dimensional motion.