PURPOSE: To provide a smoke-controlling compsn. which controls the amount of harmful gas emitted during burning while retaining flame retardance, consisting of a specified compd. and a metal hydroxide.

CONSTITUTION: Optically, 20W80wt% hydroxide [e.g. Mg(OH)2] of a metal selected from among Group IIA and/or IIIA metals of the Periodic Table is blended with a compd. which emits at least one compd. selected from among sulfur compds, nitrogen compds., phosphorus compds. and halogen-contg. compds. (e.g. SO2, H2SO3, NO, NO2, H3PO3 or HCl) by thermal decomposition or burning reaction, or with an org. high-molecular compd. (e.g. PVC) contg. said compd.