Abstract: Late Triassic magmatism in the Indochina Block is significance for understanding the tectonic regime and transition following the closure of the Eastern Paleotethys Ocean. However, previous studies have predominantly focused on western Yunnan and Thailand-Laos-Vietnam region. The petrogenesis and geodynamic mechanisms of contemporaneous granitic rocks extending southward into the Cambodia remain poorly constrained, and their relationship with the giant Eastern Paleotethyan igneous belt has not been effectively defined. Therefore, this study, through systematic field investigations, zircon U-Pb geochronology, and whole-rock elemental and isotopic geochemical analyses, systematically reveals the source characteristics and tectonic affinity of the Kchol granites in western Cambodia and provides a new evidence for the post-collisional evolution and extension of the Eastern Paleotethyan tectonic domain. Research suggests that the granitoid rocks in western Cambodia are primarily composed of biotite monzogranite and granodiorite, with zircon U-Pb ages of 209-203 Ma, belonging to the late Late Triassic. The biotite monzogranite samples are high-K calc-alkaline, with SiO₂ contents of 69.7%-72.0%, K₂O contents of 3.24%-5.35%, zircon in-situ ε_Hf(t) values ranging from -2.2 to +12.7, and ε_Nd(t) values of -4.2 to -1.5. In contrast, the granodiorite samples have SiO₂ of 63.1%-63.5%, and K₂O of 2.25%-3.04%, with ε_Hf(t) values of +0.4 to +5.4, and ε_Nd(t) value of -2.6. Geochemical characteristics indicate that these Late Triassic granitoids are medium- to highly-fractionated I-type granites. Their source is characterized by a hybrid nature, dominated by juvenile mafic lower crust with a subordinate contribution from metasedimentary rocks. These granites are interpreted as the products of partial melting of the lower crust, triggered by asthenospheric upwelling in a post-collisional setting following the closure of the Paleo-Tethys Ocean and the collision between the Sibumasu and Indochina blocks. Regional geological data and geochronological comparisons reveal a magmatic sequence in the Eastern Granite Province spanning from ~230 Ma to ~200 Ma. This indicates that the Kchol granite in western Cambodia may represent an eastward extension of the Eastern Granite Province within the giant Eastern Paleotethyan igneous belt. They likely responded to a post-collisional deep geodynamic process in the Eastern Paleo-Tethys.