The preparation conditions for both a high yield without aggregation and a small mean-size of chitosanfucoidan nanoparticles were sought by a screening method, i.e., discarding the ones satisfying neither of both to prepare them by polyelectrolyte complexation with chitosan and fucoidan. The effect of the pH level of chitosan solution and the chitosan-fucoidan mass ratio was investigated on the following aspects: the turbidity and aggregation pattern of suspension, the yield of dried mass, electrostatic interaction, fucoidan loading efficiency, the particle size distribution and the morphology of the polyelectrolyte complex prepared by polyelectrolyte complexation between chitosan and fucoidan. The mean size of prepared nanoparticle ranges between 365-900 nm. The nanoparticles tended to grow as the pH of chitosan was increased up to 3.69, after which they became smaller. This pattern of growth is prominent as the mass ratio of chitosan and fucoidan decrease. The conditions of pH 5 and 1 : 1 chitosan-fucoidan mass ratio were suggested as ad hoc optimum conditions by the screening method to prepare chitosan-fucoidan nanoparticles for high yield, small size and good suspension stability. They were almost consistent with the optimum conditions for the maximum value of chitosan-fucoidan nanoparticles prepared per unit input mass, which were analyzed by response surface methodology (RSM).