  We report on timing and spectral observations of the microquasar XTE
J1550-564 during its 2000 outburst made by the Rossi X-ray Timing Experiment
(RXTE). We study the spectral properties of the source during both the rise to
the outburst and its decline. We observe transitions from a low hard state to
an intermediate state, and vice versa, before the source returns to quiescence.
We show that the first transition likely reflects a change in the relative
importance of the emitting media, instead of a change in the total accretion
rate, contrary to the second transition.
  We investigate the temporal properties of the source, and follow the
evolution of a low frequency Quasi Periodic Oscillations (QPO).
