This study investigates the workpiece temperature in minimum quantity lubrication (MQL) deep-hole drilling. An FEA-based inverse heat transfer model is developed to estimate the heat generation based on temperature inputs from embedded thermocouples. The temperature distribution in the workpiece is then calculated by the inverse solutions. The method is validated experimentally using a 10 mm carbide drill drilling cylindrical iron workpiece under both dry and MQL conditions. The calculated temperature distribution shows good agreement with experimental temperature measurements. This study demonstrates that the heat generated on the hole wall surface is as significant in workpiece temperature as that on the hole bottom surface in deep-hole drilling.