Prediction of groundwater inflow rates to an open pit is an important issue because unexpected flows can cause safety and environmental problems. This paper presents groundwater inflow rates to an open pit mine developed in metasediment and diorite in Eastern Turkey. Representative hydrogeological conceptual model was developed based on data collected from field studies and subsequently it was transferred to a two dimensional numerical model through SEEP/W of GeoStudio. After construction of model grid and assignment of hydraulic properties along a selected critical cross section, calibration of the model was conducted under steady-state conditions by trial and error. The root mean square error was calculated as 6.54 meter, 93.56 kPa and 9.57 meter for total hydraulic head, pore water pressure and pressure head values, respectively. The steady state calibration was followed by transient analyses for twenty years to confirm the simulated steady-state values. Results show that transient run in the long term reached a steady-state condition which was not significantly different than the generated steady-state solution, thus confirming the adequacy of the model for estimation of groundwater inflow rates. The groundwater inflow rates were predicted by running the model under transient conditions over a two-month period during which the material from the open pit has been removed. The results of each phase represented initial conditions for the subsequent phases. The results for a one-year simulation show a sudden increase in the inflow rates through the pit bottom when its elevation is lowered by 50 meters. As the pit bottom deepens, groundwater inflow through east and west slopes also increased. Hence, increase in groundwater inflow from east and east slopes indicates that a drainage scheme must be designed for both slopes.