Abstract : A study was initiated to clarify the behavior of biaxial fatigue cracking from a notch, transverse or 45 deg inclined, in a cruciform specimen of a 7075-T651 aluminum alloy. The biaxial fatigue test was conducted in air and aqueous 3.5% NaCl solution at room temperature under inphase and 180 deg out-of-phase loadings with biaxiality ratios, ranging from 0 to 1.5. Under in-phase loading, a greater biaxiality ratio extended the fatigue life and reduced the fatigue crack growth rate in both environments. On the other hand, under 180 deg out-of-phase loading, a greater biaxiality ratio shortened the fatigue life and increased the fatigue crack growth rate in both environments. Under the loadings of both phases, the fatigue growth life was shorter and the fatigue crack growth rate was greater in 3.5% NaCl solution than in air at a given biaxiality ratio. Such features evidence the acceleration of biaxial fatigue crack growth by 180 deg out-of-phase loading or/and by 3.5% NaCl solution. SEM fractographs of the biaxial fatigue crack surfaces showed ductile and brittle striations in the specimen fatigue-tested in air, and a mixture of both striations and intergranular cracking in the specimen fatigue-tested in 3.5% NaCl solution. Such fractographic features show the striation formation in air and a mixture of striation formation and intergranular cracking in 3.5% NaCl solution under biaxial fatigue loading. The biaxial fatigue crack growth rate, determined experimentally, was in partial agreement with that predicted by some reported models.