We study the colloids of gold nanoparticles (GNPs) covered with water-soluble natural branched polysaccharide arabinogalactan (ARB) which is used as reducing and capping agent in the GNPs colloidal synthesis. A set of the ARB-GNP composites with gold content ranging from 3.1 to 11.9% was investigated. Transmission electron microscopy of dried colloids shows that the clustering of spherical GNPs into dimers and trimers increases with the gold content. The ARB-GNP colloids are studied by static and dynamic light scattering resonantly enhanced by the GNP surface plasmons. The GNPs clustering within the colloids is manifested by the scattered light depolarization. Spherical form of the colloids is proved by the analysis of their translational and rotational diffusion coefficients obtained via dynamic light scattering.