The main object of the invention is to obtain LiMnPO.sub.4 having an excellent crystalline and a high purity at a lower temperature. The present invention provides a method for manufacturing LiMnPO4 including the steps of: precipitating for obtaining precipitate of manganese hydroxide (Mn(OH).sub.x) by adding a precipitant to a Mn source solution in which a Mn source is dissolved; reducing for obtaining a reduced dispersion solution by dispersing the precipitate in a reducing solvent; adding for obtaining an added dispersion solution by adding a Li source solution and a P source solution to the reduced dispersion solution; pH adjusting for adjusting the pH of the added dispersion solution in the range of 3 to 6 to obtain a pH-adjusted dispersion solution; and synthesizing for synthesizing by reacting the pH-controlled dispersion solution by a heating under pressure condition.