Angular microvibrations of platform jitter on a three-axis attitude-stabilized satellite are measured in space using an onboard laser communication terminal. Stable optical tracking control allows the measurement of relative angular variations from the reference line of sight of the optical link. The tracking accuracy in this measurement is less than 1 μrad rms. The angular variation and the drift rate on the satellite are measured at a sampling rate of 500 Hz, and these data are downlinked to a ground station via a satellite-to-ground optical communication link. The power spectral density of the satellite microvibration is calculated by a Fourier transform analysis. The frequency spectrum of the gimbal mirror’s angular variation is also obtained when the coarse tracking control is operational. The rms value agrees with the residual coarse tracking error estimated before launch of the satellite. These results will be useful for the future design of a tracking control loop for optical communication systems. © 2001 Society of Photo-Optical Instrumentation Engineers.