Based on analyses of the sampled shales of field outcrops and well cuttings, the authors studied the geochemical characteristics of the shales of Mesoproterozoic Xiamaling Formation in Beijing. Al₂O₃, Na₂O and K₂O are depleted whereas SiO₂, TiO₂ and Fe₂O₃^T are relatively enriched. The shales show homogeneous REE content, relatively enrichment of LREE and depletion of HREE,obvious negative Eu anomaly, and slightly negative Ce anomaly. The REE distribution patterns from different shale samples showing an affinity reveal that they have the same source rocks including granitic, dioritoid and mafic rocks from the upper continental crust of Inner Mongolia uplift, and the ratios of trace elements show these features too. They were deposited in a reducing environment with relatively deep water. The tectonic setting of the source area seems to have been a continental island arc.