PURPOSE: To provide the title composition capable of preventing instruments from corrosion by freeing of evolution of a toxic halogen-contg. gas on combustion, comprising halogen-free polymer(s), a heat-expandable graphite, and an inorganic water-contg. compound (or its mixture with a siutering inorganic filler).

CONSTITUTION: The objective composition comprising (A) 100 parts by wt. of halogen-free polymer(s), (B) 3W120 parts by wt. of a heat-expandable graphite, (C) 10W200 parts by wt. of an inorganic water-contg. compound or of its mixture with a sintering inorganic filler. The component (A) is, e.g., polyethylene, ethylene- propylene rubber, phenol. The component (B) is a graphite obtained by oxidation with nitric acid, etc., or by electrolytic oxidation of a highly-crystalline natrurally- occurring graphite, having a bulk density of 0.2W0.5, an expansion ratio of several- several hundreds times, and a water content of 5wt% or less. The component (C) is, e.g., Al(OH)3, talc.