Interpolyelectrolyte complexes (IPECs) were obtained by the mixture of solutions of chitosan and poly(sodium 4-styrene-sulfonate). The resultant dispersions were characterized using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Gyration radius from SAXS increased as sulfonate to aminium molar ratio, rSA, increased, while pair distance distributions, P(r), shifted to higher values of r, describing the process of particle formation as resultant from collapse of solubilized IPEC clusters in the form of solid particles, followed by nucleation of larger ones. Intensity correlation curves from DLS were used to obtain parameters related to Brownian motion of (or within) IPEC clusters. IPEC cluster dimension growth was related to characteristic relaxation rate and relaxation rate distribution width. Association of DLS-derived results to SAXS-resultant data yielded a description of nanoparticles made of solid IPEC clusters stabilized by solubilized IPEC species.