Naturally occurred radiocarbon (14C), as a powerful tool, has been used for decades for archeological and geological dating. Recent development and applications of Accelerator Mass Spectrometry (AMS) have made it possible to detect 14C at its natural abundance in very limited sample sizes (<mg C). This has greatly increased the range of applications using 14C in natural science, particularly in the Earth sciences. In this paper, we briefly reviewed the principal and some recent applications of using natural 14C in marine geochemical studies mainly in three areas:①14C studies of carbon cycling in the ocean; ②Using 14C as a tracer to determine the sources, transformation and turn over of the major organic compound classes in different organic carbon pools in the ocean; and ③14C studies of compound-specific biomarkers in marine sediments. These studies have shown novel results and demonstrated that natural radiocarbon measurements at compound level provide a new and sensitive tool for determining the sources, transformation and biogeochemical processes of carbon cycle in oceans in the past and at present both at large and small scales.