Aerodynamic instabilities are one of the most important issues for compressor designers. Many experimental works have already studied these instabilities that occur around the maximum of the total-to-total pressure ratio. However, the basic mechanisms of these flow phenomena are not yet fully understood. Usually the first instability encountered in most compressors is rotating stall that is characterized by one or more cells of stalled flow that rotate at a fraction of the rotor speed. This instability is usually responsible for a performance reduction (efficiency, pressure ratio, etc.) and large vibrations that reduce the blade life duration. Moreover, it can induce surge, a low frequency instability that leads to a mechanical failure of the whole system. In order to avoid such instabilities, designers usually apply a safety margin called the ‘‘surge margin”. Unfortunately, this strong constraint limits the efficiency and leads to an over dimensioning of the compression system. The possibility to reduce the surge margin is thus of a great interest for designers. However, operation closer to the stability limit increases the probability of stall inception. The losses accompanied with instabilities decrease life duration and performance of compressors. It is anticipated that surface roughness may reduce compressor performance, although it may enhance surge characteristics of compressor stages. Surface roughness increases significantly due to erosion, corrosion, and deposition during operation under high pressure and temperature condition and even exists on new made blades. However, the partial increase of roughness may also restrain flow separation and reduce flow loss. It is necessary to explore methods that will lower compressor deterioration, thereby improving the overall performance. In this paper, one-state of an axial compressor of a turbo-shaft engine is computationally investigated. Numerical results are obtained in three dimensions using a finite volume solver for incompressible RANS equations with SST turbulence modeling. Effects of surface roughness on performance and instabilities of the stage in different rotational speeds have been explored. In high rotational speeds from to , increasing surface-roughness will improve the surge margin at the cost of lower efficiency of the stage; however in lower rotational speed than there is an unexpected phenomenon of improving surge margin simultaneously by increasing efficiency of the stage. These results also show that the main effect of instability is to decrease flow rate hence to decrease the stage compression ratio. Therefore, different combination of uniform and non-uniform surface roughness on rotor and stator blades was examined. Computational results revealed that the rotor has contributed higher effects on the performance of compressor. In particular, the effects of roughness on pressure surface are higher than suction surfaces of blades. The effects of variable roughness on rotor blade surfaces in span-wise direction were also examined which show significant effects on work redistribution along rotor blades. It has been found that for the functions with increasing values from root to tip aerodynamic performance and efficiency have better conditions. These may have important desirable effects on design of compressor stages with improved surge margin and efficiency Keywords: Axial compressor, Surge, Stall, Surface roughness, Efficiency, Rotational speed