The method for synthesizing indium phosphide nanoparticles using indium trichloride as an indium raw material and tris(dimethylamino)phosphine as a phosphorus raw material, includes a preparation step of mixing the indium raw material, the phosphorus raw material, an organic solvent having a boiling point of 170° C. or higher, and a particle surface ligand to obtain a mixture solution and a synthesis step of synthesizing the indium phosphide nanoparticles by heating the mixture solution to 150° C. or higher but lower than 170° C. In the method, the particle surface ligand is an aliphatic amine having a carbon number of 18 or more, and the indium trichloride is an anhydride.