High quality CoFe₂O₄ nanoparticles were synthesized only in 16 min, continuously in two coupled microreactors. The first microreactor induced the fast homogenization of the reagents mixture at ambient temperature so Fe³⁺ and Co²⁺ hydroxides precipitate, while a second microreactor heated at 98 °C allowed the fast aging and the evolution of amorphous hydroxides into faceted and crystalline CoFe₂O₄.