This work is in addition to the various works undertaken by the researchers, using biomass as adsorbent. However, the aim of this study is the recovery of a marine material alga: Ulva lactuca) that we were able to transform into adsorbent with treatment under physical carbonization and chemical activation. The ability of treated and untreated Ulvala ctuca, to remove hexavalent chromium Cr (VI) ions in aqueous solutions was investigated. The influence of pH, sorbent dose, initial concentration, temperature, and contact time has been studied in batch process. The materials are characterized by FTIR and SEM analysis. The highest Cr (VI) removals (100%) were achieved at pH of 3, particle size of less than 250μm, dose of 1 g/L, and equilibrium time of 180 minutes. Thermodynamic results indicated that the Cr (VI) adsorption process was spontaneous and exothermic. The adsorption data fit well with Langmuir isotherm model with a maximum adsorption capacities (qmax) of untreated and treated Ulva lactuca were between 0.6 and 2 mg/g. Higher Cr (VI) removal revealed the practical applicability of Ulva lactuca in water and wastewater treatment systems.