Reverse micelle (RM) based synthesis of carbon-supported perovskite type oxide (LaMnO3) was investigated. By using cyclohexane as oil phase, six kinds of nonionic surfactants were tested for the formation of the revere micelle dispersions containing aqueous solutions of mixed nitrates of La3+ and Mn2+ (RM-N) and tetramethylammonium hydroxide (RM-A) at the water/surfactant molar ratio (R-W) of 3. RM-A was found to be more difficult to form compared with RM-N or the RM containing pure water. At a temperature range of 5-25degreesC, it was given only by the surfactants with hydrophilic-lipophilic balance (HLB) values of 10.0-10.9. Phase diagrams of oil-surfactant-alkaline solution (or pure water) were constructed at 5 and 15degreesC for the best two surfactants, i.e., poly-(oxyetylene)(6)-nonylphenyl ether and poly-(oxyetylene)(5)-lauryl ether. Mixing RM-N and RM-A together gave the RM containing a mixed hydroxides-precursor (RM-P), which was further converted into carbon-supported LaMnO3 through a series of treatments including the addition of carbon powder and calcination in N-2 atmosphere at 600degreesC. The size of RM-P as well as that of the LaMnO3 grains supported on carbon could be controlled well by selecting R-W. The carbon-supported LaMnO3 proved to be highly active for the electrochemical reduction of oxygen. (C) 2004 The Electrochemical Society.