Na alginate was crosslinked in aq. sal. (concn. 0.5-2%) at 4 degrees C or 21 degrees C with CaCl2 (concn. 0.1 or 0.5 M) to alginate hydro gels with good mech. properties and compact structure. Reaction dynamics, swelling degree, ultrastructure and mech. strength of the hydro gels were detd. Hardness, guminess and masticability of the hydro gels increased with the increasing Na alginate concn. and crosslinking temp.