It is known that when an axial flow compressor running at constant speed is throttled down, a phenomenon of rotating stall may occur in one or several intermediate stages. The velocity of propagation of the latter phenomenon has to be investigated as it determines the frequency of the blade vibrations excited by this non-steady stall. This investigation was carried out on a single rotor. The similarity laws in the working region associated with rotating stall were found and the similarity laws relative to the velocity of propagation of stall were also determined when a discontinuity in the characteristic curve was associated with this phenomenon. It is also shown that the velocity of rotating stall may be determined from an induced phenomenon: sound or vibration analysis.