This study examined the effects and interactions of cobalt ion concentration, reducing agent to cobalt ion ratio, and water to surfactant ratio on the particle size and polydispersity of cobalt nanoparticles of 1-5 nm diameter synthesized via reverse micelle method. Characterization methods include tapping mode atomic force microscopy (TMAFM) and dynamic light scattering. The effects and interactions were determined from a statistical treatment of the statistically designed 3-factor 2-level full factorial experiment. The main effects were determined for particle diameter and polydispersity. Additionally, one set of significant two-factor interactions were determined for the diameter and three sets of significant two-factor interactions for the peak width.School of Chemical Engineerin