A study was carried out to determine arsenic species in Porphyra seaweed originating from the ChinaSea. Information about arsenic species in Porphyra was provided by HPLC-ICP-MS and ES-MSMS.The total arsenic concentrations of Porphyra samples from five different producing areas rangedfrom 2.1 to 21.6mg/kg. The analysis report also showed that arsenosugars were the only arsenicspecies that could be detected in all of the extracts of samples. Arsenosugar PO4 was the majorcompound in most samples (0.3-13.9mg/kg of dry weight), followed by arsenosugar OH (0.7-6.2mg/kg of dry weight). A further experiment was done to investigate the stability of arsenosugars inthe process of being heated. It was observed that the arsenosugars were stable during a short-termheating at 100℃. Their stability in human ingestion was also studied. A substantial increase ofdimethylarsinic acid (DMA) was detected in urine samples collected from six volunteers after theconsumption of this seaweed. The results obtained indicated that arsenosugars had been metabolizedto DMA, which is more toxic than arsenosugars. From this point of view, consumers should considerthe possible adverse effects of edible Porphyra on human health and choose those Porphyra havinglower arsenic concentrations.