In the last decade, novel strategies to synthesize polydopamine nanoparticles (PDA NPs) have been continuously developed owing to the applications of this synthetic melanin analog in nanotechnology. However, producing them on a large scale continues to be a challenge and, to achieve this purpose, the ability to control and predict PDA NP size and morphology is essential. For this reason, in this work, the formation kinetics of PDA NPs produced by dopamine oxidative polymerization were analyzed as a function of the alkalinity degree (ammonium hydroxide concentration) and the type of alcohol (ethanol or 2-propanol) used in the synthesis medium. It was found that PDA NPs underwent nucleation/growth during polymerization, and a simple mathematical model was proposed to predict PDA NP diameter depending on the reaction time and the alkalinity degree. Moreover, with the aim of optimizing the reaction time without altering the main physicochemical properties, PDA NPs obtained after four different times (1, 3, 5 and 24 hours) were characterized. It was shown that reducing the PDA NP synthesis time from 24 to 3 hours was possible without altering either their Fe³⁺-chelation capacity or their antineoplastic activity, which are two of the properties that make them a revelant material for nanomedicine studies.