It is widely known that arsenic is highly toxic to humans, and the chronic exposure to this element produces various damages to the health of people. In Peru have been reported particularly high levels in rivers of the south coast. Objective. Evaluate two analytical techniques of speciation of the two forms of inorganic arsenic in river water of Tacna, in southern Peru. Material and methods. Developed a comparative study of the technique of separation by anion-exchange resin and ion chromatography for the speciation of arsenic (V) and arsenic (III) in water samples from four rivers of the Pacific slope in two districts of the region Tacna. The total amount of arsenic was determined with flow injection system with atomic absorption attended. Results. We obtained a good degree of separation in both procedures, however, the technique of anionic exchange resins have a lower detection limit of ion chromatography, 2.0 mg/L and 32 mg/L, respectively. In four of the six samples were higher than those recommended by the Environmental Protection Agency of the united States, and they succeeded in determining the amounts of arsenic (III) and arsenic (V). Conclusions. Both techniques can be considered applicable for different types of water; nevertheless, the technique of separation by anion-exchange resin has higher detection sensitivity than the technique of separation by arsenic ion chromatography; and allows a high degree of speciation of inorganic arsenic in samples of river water.