Abstarct: One of the most difficult issue in target motion analysis is bearing only target tracking (BOT), which basically is used in under water targets tracking with passive sonar sensor. Generally, Kalman baxsed method are used in state estimation of target motion in bearing only target tracking. However condition such as maneuver in target motion and unknown statistical parameters of measurement noise, degrade the performance of these methods. In this thesis Fuzzy Unscented Kalman Filter which is incorporation of fuzzy logic and Unscented Kalman Filter, is proposed. Fuzzy system is used to adjust the covariance matrix of measurement and process noise. In comparision with Unscented Kalman Filter proposed method has reduced the estimation error of tracking. The authenticity of the claim is confirmed in simulation.