Abstract: An extended Kalman filter is used to determine the major aerodynamic coefficients of a re-entry body in this paper. The emphasis is put on estimating the states and parameters only on the basis of the re-entry on-board measurement data in the absence of trajectory observation data. The measured data include angular rates and acceleration obtained from the rate gyros and acce-lerometers installed in the vehicle. A mathematical model presented is based u-pon the 6-degree-of-freedom motion equations. Both ballistic and maneuvering re-entries are considered. The numerical simulation and real data extraction show that the presented method can provide satisfactory results.