The thermoreversible gelation of κ-carrageenan (KC) was studied by small angle laser light scattering (SALLS). The mobility of random fluctuation of scattering speckles is used to detect the sol-gel transition

and the mobility disappears suddenly at a point during the cooling process of KC solutions．The temperature at that point is designed as gelation point (Tgel)．Effects of several counterions

including Na+

K+

NH4+

Ca2+

Cu2+ and Zn2+

on Tgel were determined. Although all ions are able to promote the gelation of KC

the promoting ability can be ranged to three resions：K+

NH+4 (I)

Ca2+

Cu2+

Zn2+(II) and Na+(III)

their promoting abilities have the following sequence：I＞II＞lII. Tgel is found to be proportional to the square root of concentrations of conterions

except Na+．The influence of KC concentration on Tgel in NaCl and KCl aqueous solutions also shows the promoting abilities of both Na+ and K+ ions．Furthermore

the phase diagram of KC-KCl aqueous solutions at 30℃ was obtained. The comparison of Tgel values for KC-NaCl solutions before and after dialysis further reveals the promoting function of Na+ ions

and some controversial results in literature concerning the function of Na+ ions ale supposed to result from the different methods used for Tgel determination．