The sedimentation of a similarly charged monodisperse colloidal suspension was studied to investigate the role of collective particle interactions affecting the rate of sedimentation and thereby the stability. The particle concentration profiles, microstructure formation, and the sedimentation rates were determined using a nondestructive back-light scattering technique. Stochastic particle dynamics simulations using the Beresford-Smith and Derjaguin-Landau-Verwey-Overbeek repulsive pair potentials were carried out to predict the sedimentation rates. In addition, Monte Carlo simulations were performed to reveal the particle microstructure formation. The collective particle interactions result in an oscillatory effective potential of interaction between the identically charged particles, even though the pair potential is repulsive, and lead to a more ordered microstructure formation and reduction in the sedimentation rate. The theoretical predictions, which were in good agreement with the experimental measurements, clearly showed the importance of the collective particle interaction effect in stabilizing the monodisperse suspension.