Accelerator mass spectrometry (AMS) is an ultrasensitive measure for tracing 14C labeled molecules in vivo or detecting the biomarker for assessment of carcino-genesis. In this review, basic principles, wide applications and new progresses of 14C-bio-AMS are presented. It has been a new advanced tool for measuring the adduction of biologcial molecules with xenobiotics, including carcinogens, drugs, agrochemicals, nicotine, etc. The successful applications have proven the effectiveness of AMS to assessing cancer risk, screening drug toxicity and studying nutrients uptake. In particular, AMS is characterized by measuring xenobiotics at very low dose levels relevant to human environmental exposure. It is sensitive and precise to an attomole (10~18 mole) or less of 14C per mg carbon. Although it has some shortcomings, undoubtedly, AMS possesses an evident merit of high sensitivity and will have widespread applications in the biomedical sciences.