We have studied the evolution in time of the structure factor of aggregating kappa-carrageenan using light scattering. Aggregation was induced by cooling solutions containing 0.01 M KCl below a critical temperature. The ionic strength of the solutions was fixed by adding 0.1 M NaCl. Large aggregates consist of locally rigid bundles formed by parallel aggregation of kappa-carrageenan. The effect of concentration (C < 0.3 g/L) and temperature on the structure was found to be small. The aggregation rate increases with increasing concentration and decreasing temperature. The optical rotation, i.e., the helix content, is not influenced by aggregation. The molar mass, size, and interactions of nonaggregated kappa-carrageenan were determined in the coil and the helix state. For the large molar sample used in this study (M-w = 4.2 x 10(5) g/mol) the molar mass and the size are almost the same in the coil and the helix state.