According to this invention, an amorphous or pseudo-boehmite-type hydrated alumina gel and an alkali metal carbonate or bicarbonate as starting materials are reacted in an aqueous medium to give a method of producing a process for producing an alkali aluminum complex hydroxide carbonate salt which is industrially low-cost and has high productivity. Furthermore, by using a gibbsite-type hydrated alumina, a lithium aluminum complex hydroxide carbonate salt can be synthesized by a migration method. The lithium aluminum complex hydroxide carbonate salt and the sodium aluminum complex hydroxide carbonate salt obtained by the processes of the present invention have excellent compoundability in pigments and resins. In addition, these complex salts have no foaming hazards at the time of processing the resins and are useful as resin fillers for halogen capturing property, infrared ray absorbing property and excellent transparency. They are especially useful as a stabilizer (halogen capturing agent) for resin films, a warmth-keeping agent (infrared absorbing agent) and an anti-blocking agent.
