Biaxial fatigue behaviour of ISO AlMgO.5Si alloy (6060-T6) tubular welded specimens under in-phase torsion-bending and constant amplitude loading was investigated. The tests were performed using a standard servo-hydraulic machine with an adequate gripping system. A finite element analysis was performed in order to obtain both in-bending and in-torsion stress concentration factors at weld root, k(tb) and k(tt) respectively. Fatigue lives were correlated with the von Mises equivalent stress. All results are placed in same scatter band independently of the B/T and R ratios, confirming that von Mises equivalent stress (Deltasigma(eq)/2) gives good correlation in the case of multiaxial proportional loading, taking in account the normal data scatter observed in fatigue results of welded joints.