The variation of permeability of typical petroleum cement paste is investigated as functions of mechanical loading and chemical degradation under the temperature of 90A degrees C. In sound material, the permeability classically increases with deviatoric stress due to microcracks and volumetric dilatancy but decreases with confining pressure. Chemical leaching leads to significant increase of porosity of cement paste. However, the permeability of degraded material is lower than that of sound material during triaxial compression tests; this is due to compaction of pores under confining pressure. Further, the permeability variation in degraded cement is much more sensitive to confining pressure than that of sound material. During triaxial creep test, the permeability of degraded material decreases with time while that of sound material increases; this shows that the chemically leached material has a higher potential of volumetric compaction which is a key mechanism of plastic deformation. Coupled chemical degradation and triaxial compression tests are also performed. Under low confining pressure (3 MPa), the permeability increases with propagation of leaching front, and there is formation of preferential flow paths in the axial direction. However, with high confining pressure (10 MPa), there is no increase of permeability during chemical leaching and creation of successive degraded layers in the flow direction.