Hydrocyclones consist basically of a cylindrical part associated to a conical region for solid-liquid and liquid-liquid separation in centrifugal field. The geometric dimensions of each part are important in the separation process, being related to capacity and classification power of equipment. Thus, this paper aims to propose a systematic strategy to determine the geometric dimensions by formulating an optimization problem using the Firefly Colony Algorithm in the multi-objective optimization context. From the obtained results it was possible to find a hydrocyclone design capable of providing both high overall efficiency (E-T) associated with low Euler number (Eu) and underflow-to-throughput ratio (R-L).