Managing radioactivity caused by thorium (Th) and uranium (U) is a critical challenge in rare earth element (REE) hydrometallurgy. Sulfuric acid baking followed by water leaching is one of the most widely adopted industrial routes in REE processing; conventional Th-U separation within this process either relies on high-temperature acid baking (>300 °C) to form insoluble thorium pyrophosphate or requires dedicated downstream purification steps after co-leaching. This study presents an innovative approach to selectively separate Th from U directly within a single water-leaching step by optimizing leaching parameters without high-temperature acid baking. A REE pre-concentrate from the Eskişehir-Beylikova deposit was acid-baked under moderate conditions (250 oC) for 60 min with a 1:1 acid-to-sample ratio and subsequently water-leached under high pulp density (S/L = 1:2). The effects of leaching temperature (25-90 °C) and time (15-120 min) on Th and U dissolution behavior were systematically investigated. Mineral Liberation Analysis (MLA) confirmed that Th and U were exclusively hosted by distinct mineral phases, Th-parisite and plumbophyrochlore, respectively. The experimental results demonstrated that U dissolution was temperature and time-independent, maintaining a stable extraction of 90% due to soluble uranyl sulfate formation. In contrast, Th recovery sharply declined to <10% at 90 oC due to the temperature-dependent decrease in stability of Th-sulfate complexes. A recovery ratio (RR) of approximately 13.3 (RR = %U/%Th recovery) was achieved within the water leaching step alone, demonstrating that Th-U separation can be completed at the leaching stage, thereby reducing process complexity and the number of required unit operations.