Predictable and repeatable outcome is a major issue in nanoparticle synthesis. Traditionally, chemists rely on the one-factor-at-a-time method to investigate and optimise synthetic processes; however, this method is inefficient and often misleading. Design of Experiments (DoE), in contrast, can provide a greater amount of information in fewer experiments and lends itself to producing more reproducible results. Nevertheless, DoE techniques are only used by a relatively low number of practitioners in nanoparticle research. Here, we provide a case study on the synthesis of oleylamine-capped gold nanoparticles (AuNPs). Through the use of DoE, we achieved a marked reduction in dispersity and developed a model to carefully control the mean diameter of the nanoparticle populations.