In order to investigate the geochemical characteristics and sources of oil sands recently discovered in the Yanghugou Formation of the YT2 well in the western margin of Ordos basin, biomarkers and carbon isotope of the oil sands were analyzed by gas chromatography- mass spectrometry (GC/MS) and isotope mass spectrometry respectively. The results show that the normal alkanes in the oil sands displayed a significant unimodal distribution pattern with nC17 as the major peak; the value of Pr/Ph ratio was 0. 90, and the values of Pr/nC17 and Ph/nC18 ratios were 0. 30 and 0. 46 respectively. These indicate that the source rock of the oil sands was deposited in reducing conditions. Tricyclic terpanes have a relatively high content, with C23 tricyclic terpanes as the main peak and showing approximate normal distribution characteristics; the content of C27 regular steranes is higher than C29 regular steranes; the value of hopanes/steranes ratio is relatively low, which indicate that organic matters were dominated by lower algae; and the carbon isotopes of saturated and aromatic fractions are -31. 5‰ and -30. 5‰ respectively. These geochemical characteristics of the oil sands from the YT2 well indicate that it originated from marine source rocks, which means that marine crude oil was discovered firstly in the western margin of Ordos basin. Oil to source correlation analysis with the source rocks of the Pingliang, the Yanghugou, the Yanchang, and the Yan’an Formations indicates that this oil sands may come from the Pingliang Formation marine shale.