The effect of molecular weight, particle number density, and charge ratio on the colloidal behavior of positively charged polystyrene particles (PSA) in the presence of the natural polyanion carboxymethyl cellulose (CMC) was investigated by zeta potential and light scattering measurements. For low ionic strength, a phase diagram with three distinct regimes was proposed. Flocculation is favored for R values close to 1, where R is the ratio of the total negative charge (N-tn) to the total positive charge (N-tp). Colloidal stabilization is achieved in the R range of 2.5-200 and with polyelectrolytes chain length smaller than the critical chain length (L-crit), which is the contour length corresponding to the particle mean perimeter. For R values larger than 200, isolated particles and/or doublets are present in the dispersion and with polyelectrolytes chain length smaller than L-crit, whereas doublets and/or aggregates are observed when the polyelectrolytes chain length is larger than L-crit. The effect of the particle number density on the colloidal stabilization was weak. The adsorption behavior of CMC onto PSA particles was not comparable to that of CMC onto PSA films.