The mass transfer of europium(III) from an aqueous to an organic phase was studied in a quartz microchannel (internal diameter of 200 mu m) using a novel micro Laser Induced Fluorescence (micro-LIF) technique. Europium (III) was extracted from a 1 M nitric acid solution into an organic solution of TBP(1.2 M)/CMPO(0.2 M) in Exxsol D80. For the flow rates investigated plug flow was established. An experimental and data processing methodology was developed to calculate concentration profiles from the fluorescing light intensity profiles in both phases at different locations along the microchannel. In particular, the effect that the high light intensity of the organic phase has on the measurements in the aqueous phase was taken into account. Mass transfer was found to be significant in the beginning of the channel close to the inlet (1 mm distance) with extraction percentages varying between 20 and 40% depending on the total flow rate. High extraction efficiency (similar to 80%) was achieved at short residence times (in the first 6 s), while the overall volumetric mass transfer coefficients varied between 0.05 and 3.3 s(-1).