The Wulagai early Paleozoic gabbroic diorite pluton is outcropped in the East Ujimqin Banner of Inner Mongolia. It is located on the northern margin of the Xing-Meng Orogenic Belt (XMOB) and was previously referred as part of the Erenhot-East Ujimqin Paleozoic magmatic belt. This study reports zircon U-Pb age, elemental and isotopic geochemical data of the pluton, so as to reveal its petrogenesis and implications for the evolution of the XMOB. Zircon U-Pb dating yielded an weighted mean age of 499.6 ±1.2 Ma, indicating that it is the earliest intrusive pluton in Erenhot-East Ujimqin Paleozoic magmatic belt. Geochemically, the Wulagai pluton shows moderate SiO₂ (51.60%~54.28%), high Al₂O₃, depletion of magnesium and iron, and low alkali and potassium, thus belonging to calc alkali rocks. The gabbroic diorites are also enriched in LILE, depleted in HFSE, and exhibit gradual right-oblique chondrite-normalized REE patterns with unconspicuous positive europium anomalies (δEu=1.03~1.34). All the samples display depleted isotopic compositions with the data (⁸⁷Sr/⁸⁶Sr)_i=0.704 5~0.704 7 and εNd(t)=+2.71~+4.17, but the εHf(t) values of zircons (+10.8~+18.7) are much higher relative to the εNd(t) and show a Nd-Hf decoupling feature. Integrated geochemical, geochronological and Sr-Nd-Hf isotopic data suggest that the Wulagai gabbroic diorites were generated by the subduction of Paleo-Asian Ocean along the Sunid-Xilinhot island arc in early Paleozoic, and were formed at the initial stage of the subduction. The rocks originated from a mantle wedge which was mainly modified by the slab-derived melt prior to fluids, and there were also indistinct sedimentary materials in the source. The back-arc extension and opening of Hegenshan Ocean possibly led to the separation of Wulagai pluton from the Sunid-Xilinhot island arc. Along with the closure of Paleo-Asian Ocean, the pluton was ultimately isolated from the subduction zone by Hegenshan ophiolite complex.