5-Chloro-7-amino-8-hydroxyquinoline which is a 8-hydroxyquinoline derivative was synthesized and its thorium(IV) and uranium(VI) complexes have been determined. 5-Chloro-7-nitro-8-hydroxyquinoline was prepared by nitration reaction of 5-chloro-8-hydroxyquinoline in aqueous solution of nitric acid. Then 5-chloro-7-amino-8-hydroxyquinoline was synthesized by reduction with sodium dithionite. Proton-ligand stability constants of 5-chloro-7-amino-8-hydroxyquinoline and stability constants of thorium(IV) and uranium(VI) complexes forming this ligand were determined by using the Irving-Rossotti method computing the Calvin-Bjerrum pH-titration data. As a result, thorium(IV) complexes were found more stable than uranium(VI) complexes.