The complex formation of LaCl3 with dipivaloylmethane (dpm) was investigated in a view of the applicability to a rapid chemistry. It was found that the complex formation of lanthanum chloride with dpm in a gas phase was recognized and a volatile LaCl2 (dpm) which was formed by substitution of a chloride atom in LaCl3 by dpm molecule was mainly produced. A temperature dependence of LaCl2 (dpm) formation was examined and the activation energy of the reaction was deduced.