the present invention relates to a novel mg — ti — al composite metal hydroxide and to production method therefor . mg — ti — al composite hydroxide particles can be obtained by subjecting a solution containing a magnesium salt and a titanium salt to ultrasound processing and carrying out a high - temperature and high - pressure reaction with a solution containing an aluminum salt in the proportions of the metal elements comprised in the mg — ti — al composite metal hydroxide , thereby giving the advantageous effects that the halogen capturing ability is excellent and , when used in a polymer , degradation and early - staining prevention properties and transparency are outstanding .