The Gangjia granite stock is a garnet-bearing muscovite leucogranitic body emplaced in Yiwulüshan in Western Liaoning Province at the eastern segment of the Yanshan orogenic belt, North China craton. The SHRIMP U–Pb zircon age is 153 ± 5 Ma. The Gangjia granites are peraluminous with A/CNK of more than 1.14, and exhibit a tetrad effect in their REE distribution patterns, as well as non-charge-and-radius-controlled trace element behaviour. This is in contrast to the LREE-enriched patterns of the host Lüshan monzogranites. These geochemical characteristics, together with low Th/U ratios in zircon, suggest that the parental magmas for the Gangjia granites have experienced extensive magmatic differentiation, including interaction between residual melt and a coexisting high-temperature aqueous fluid. Their similar εNd(t), model ages, compatible age patterns and common volcanic arc signature in source materials between the Gangjia granites and the host Lüshan monzogranites indicate their comagmatic relationship. These unusual peraluminous leucogranites, coupled with the voluminous adakitic granites hosting them, represent typical post-orogenic magmatism developed under an intra-continental extensional tectonic regime. At the very end of the prolonged Jurassic magmatic evolution in Western Liaoning, extensive fractionation of most probably ferromagnesian phases and plagioclase from a calc-alkaline magma parental to the host Lüshan pluton, with overprint of the magmatic hydrothermal fluid, produced highly evolved peraluminous parental magmas for the Gangjia granites.