METHOD FOR PRODUCING RARE EARTH COMPLEX

PROBLEM TO BE SOLVED : To provide a method for efficiently producing a rare earth complex or its hydrate in excellent reproducibility. SOLUTION : The method for producing the rare earth complex (3) represented by formula (3) (R1 is a 1-8C alkyl group or a 1-8C fluorine-substituted alkyl group; R2 is a 1-8C alkyl group, a 1-8C fluorine-substituted alkyl group, a cyclopentadienyl group (one CH2 group in the group may be replaced with O or S) or the like) or its hydrate comprises reacting an acidic solution of a rare earth oxide (1) represented by formula (1) (Ln is a trivalent rear earth atom) with a neutral or an alkali solution of a β-diketone (2) represented by formula (2). The reaction is carried out while always keeping the reaction solution at pH ≥4 and <7 during the reaction.