Fe(III) modified sodium alginate beads (Fe(Ⅲ) modified Na) were firstly adopted as solid phase for micro-extraction of inorganic arsenic species from water samples. In combination with hydride generation-atomic fluorescent spectrometry (HG-AFS), speciation analysis of inorganic As(Ⅲ) and As(Ⅴ) in water samples could be accomplished because Fe(Ⅲ) modified Na had various micro-extraction behavior for inorganic As(Ⅲ) and As(Ⅴ) respectively. As a result, Fe(Ⅲ) modified Na could be developed into a practical solid phase for speciation analysis of inorganic As(Ⅲ) and As(Ⅴ), with the advantages of being efficient, simple, and environmental-friendly.