A sensitive fluorimetric method was developed for the determination of trace amount of europium in rare earth oxides. In the presence of gadolinium, the fluorescence of the europium complex with thenoyltrifluoroacetone and 4,7-diphenyl-1,10-phenanthroline was increased by a factor of about 2; the excitation and emission wavelengths were 346 and 613nm, respectively;the fluorescence was linear up to 1.59ng/ml of europium;and the detection limit was found to be 0.6pg/ml of europium. A general mechanism of fluorescence enhancement was proposed.