<jats:p> In saturated sandy soils liquefaction triggering is generally well-identified according to stress or strain criteria. On the contrary, the attainment of liquefaction in non-saturated sandy soils is still a cause of discussion in the scientific community. Even if the liquefaction resistance of non-saturated soils is higher than that of saturated ones, these soils may liquefy, as well. The increasing interest for cyclically mechanical behaviour of non-saturated sandy soils is due to the fact that desaturation or induced partial saturation can be used as useful mitigation techniques against soil liquefaction. Therefore, it is important to define, as accurately as possible, the attainment of liquefaction, on which depends the estimation of liquefaction resistance. The relevance of the apparent viscosity as a physically based parameter for the correct identification of the liquefaction triggering for fully saturated soils has been already demonstrated. In this paper, the viscous triggering approach has been used for non-saturated soils, processing some cyclic triaxial tests carried out on different sandy soils. The results confirm the reliability of the apparent viscosity as a liquefaction triggering parameter, showing a tight correlation with the strain liquefaction triggering criterion. Therefore, strain criterion should be preferred in non-saturated sandy soils. </jats:p>