The aim of this paper is assessing the effect of oscillation of groundwater level, which is a major input in rockslide and deep-seated gravitational slope deformation, using numerical groundwater modelling techniques. Movements of these landslides could be related to annual/seasonal changes of external factors (e.g. rainfall, snowmelt, temperature oscillations) or to human actions (e.g. impounding of landslide toe by artificial lakes, excavations). These factors can be responsible of both the initial failure as well the successive reactivation or the continuous slow motion. In our study we focused on two examples of recent or historic landslides for which a suitable dataset is available: the Mt. de La Saxe rockslide (2009–2012, Aosta valley; Italian Western Alps) and the Vajont rockslide (from 1960 to October 9th 1963). For two representative sections we developed 2D steady and transient groundwater flow models using a finite element software (FEFLOW). Hydraulic head distributions coming from the initial steady state hydrogeological models are used as base for complex transient models were time series of infiltration, resulting from precipitation, temperature, snowmelt data (La Saxe rockslide) and reservoir level (Vajont rockslide), are applied. The two examples can be useful for a better understanding of the evolution of rockslides and suggest the required set of data and modelling approaches both for seasonal and long term slope stability analyses.