Abstract: Growing interests in the determination of different arsenic species in ground waters is caused by the fact that toxic effects of arsenic are solely connected with its chemical forms and oxidation states. The toxicity and bioavailability of arsenic can only be determined if all its forms can be identified and quantified. In determinations of water samples inorganic arsenate (As (III), As (V)), methylated metabolites (MMAA, DMAA) and other organic forms such as AsB, AsC, arsenosugars or arsenic containing lipids have the most interest. Considerable analytical progress have been made toward arsenic speciation over the last few decades. Therefore, this research review the general description of the occurrence of arsenic in environment, its toxicity and measure techniques for speciation analysis. Methods based on high-performance liquid chromatography separation joined with inductively coupled mass spectrometry, hydride generation atomic spectrometry and electrospray mass spectrometry detection have shown most powerful methods for arsenic speciation in environmental and biological matrices. These methods provide strong reliability on understanding of arsenic metabolism and biological cycling.