The present invention relates to ready-to-use sterile, alginate-based, aqueous compositions for medical use. More particularly, the invention relates to an aqueous composition for medical use that has been sterilized by heat sterilization and having a viscosity at 25° C. of at least 300 cP) (Helipath® T F spindle, 100 rpm at 25° C.), said composition having a pH in the range of 6.5-7.5; containing 0.5-10 wt. % of an alginate salt; and further containing 10-500 mM of one or more dissolved C2-C7 mono- or dicarboxylates that are optionally substituted with up to 2 hydroxyl groups.The alginate-based composition of the present invention has excellent storage stability and is easy to manufacture. The alginate-based aqueous compositions of the present invention can advantageously be used, for instance, to prevent adhesions between a healing trauma site and adjacent surrounding tissue. These compositions can further be used in implants or in pharmaceutical preparations for oral administration.