A strain-based multiaxial fatigue criterion previously proposed for fatigue assessment of unnotched specimens is here extended to the case of notched ones. Such a criterion is a reformulation of the stress-based multiaxial High-Cycle Fatigue (HCF) criterion by Carpinteri and Spagnoli. The extension herein presented considers as the critical point, where to perform the fatigue assessment, the material point located at a certain distance from the notch tip, depending such a distance on both the biaxiality ratio (defined as the ratio between the applied shear stress amplitude and the normal stress amplitude) and the control volume radii R1 (related to Mode I) and R3 (related to Mode III). Some multiaxial fatigue data related to specimens made of titanium grade 5 alloy (Ti-6Al-4V) and weakened by sharp notches are examined to validate the extended criterion.