A planar microcavity using mixed a Langmuir-Blodgett film of a europium complex HDP . Eu(NTA)(4) (where HDP cetylpyridinium and NTA = alpha-naphthyltrifluoroacetone) and arachidic acid (AA) as fluorescence working material, and vacuum evaporated silver films as reflective mirrors was fabricated for the first time. Using the traditional Langmuir-Blodgett (LB) technique, the mixed Langmuir film of the Eu complex and AA on a water subphase containing 0.20 mM of Eu(ClO4)(3) was finely transferred onto a lipophilically pretreated silver mirror to form a multilayer LB film microcavity with a lambda/2 optical length (where lambda is the emission wavelength). The optical length of the microcavity was measured by a multibeam interference method. The fluorescence spectrum of the lambda/2 resonant microcavity coincides with that of the LB film of the complex, and microcavity effects such as fluorescence intensity enhancement and lifetime shortening have been observed.