Maling oilfield is one of the earliest-discovered oilfields in the Ordos basin.It is also typical representative of the pool reservoir land fluvial sandstones.However,previous study on geochemistry of crude oils and source rocks in the Maling oilfield is not enough and the genesis of crude oil depends mainly on geology suppositions.In this paper,21 crude oils from the Maling oilfield and 14 source rocks in the Ordos Basin have been systematically analyzed and geochemical characteristics of biomarkers in these samples have been studied.The distribution and composition of the biomarkers indicate that the crude oils were formed under weak reducing fresh water lacustrine environments.Besides algae,land higher plants have also made important contribution.The studied crude oils are fully developed.The comparison study shows that source the crude oils of the Maling oilfield are derived from Yanchang Formation source rocks,especially from Chang-7 subformation.