Large quantities of Early Carboniferous-Early Permian magmatic rocks are exposed on the western side of the Langshan Mountain, Inner Mongolia. The Early Carboniferous rocks mainly consist of hornblende gabbro and granodiorite outcropped on the west side of Chaogewenduer Town. The hornblende gabbros assume the form of individual guttate bodies and were cut by the granodiorite. LA-ICP-MS U-Pb dating of hornblende gabbro yielded weighted mean ²⁰⁶Pb/²³⁸U age of 329.0±2.3 Ma, while dating of two granodiorite samples yielded 331.1±0.9 Ma and 330.0±4.2 Ma respectively. The mafic mineral in granodiortie is dominated by hornblende. Whole rock geochemical data reveal that the granodiorite is calc-alkaline nature characterized by enrichment of Na₂O (3.48%~4.46%), high Na₂O/K₂O ratios (1.03~2.39) and shows good negative correlation between P₂O₅ and SiO₂. The similar Hf isotopic signature between the hornblende gabbro and the granodiorite and their behavior in elemen-tal geochemical characteristics together indicate their co-magmatic origin derived from depleted mantle which suffered from crustal contamination. The two types of rocks show similar patterns on the chondrite-normalized REE patterns, and display relatively high concentration of light rare earth elements but low content of heavy rare earth elements with minor negative Eu anomalies. The overall chemical similarities of these rocks on the primitive mantle-normalized variation diagrams suggest affinity to arc signature. In combination with the authors'work and the large scale regional exposure of hornblende gabbro+quartz diorite+ granodiorite rock assemblage, the authors hold that the Langshan area was under the tectonic setting of continental margin arc during Early Carboniferous.