Rare earth elements (REEs) are crucial for numerous advanced industrial applications, yet their separation still presents significant challenges, necessitating innovative approaches. This study explores a novel method for the separation and purification of mixtures of lanthanum (La) and cerium (Ce) through in situ electrochemical oxidation combined with solvent extraction in a continuous microfluidic system. Specifically, the selective oxidation of Ce3+ to Ce4+ and its simultaneous extraction is demonstrated in a microfluidic cell. This method enables highly efficient La/Ce separation in a single extraction step. The microfluidic system was fabricated using additive manufacturing technology, and various process parameters were systematically investigated, including channel size, flow velocity, extraction agent type and concentration, feed concentration, and current density for electrolysis. Employing di(2-ethylhexyl) phosphoric acid (D2EHPA) in n-octane, cerium extraction rates exceeded 85% in a single step, with no detectable transfer of La3+ to the organic phase. This result underscores the effectiveness of the method in achieving a high degree of separation for these elements.