PURPOSE: To obtain a conductive sealing medium composition that has excellent electromagnetic wave shielding performance, is good in workability, and hardly sags, by incorporating a modified polysulfide polymer or a modified silicone polymer, its hardening catalyst, and an aniline polymer.

CONSTITUTION: This conductive sealing medium composition contains a modified polysulfide polymer (e.g. a compound of formula I wherein R1 to R4 each represent a bivalent organic group and (n) is a positive number), its hardening catalyst (e.g. a compound of formula II wherein R5 and R6 each represent H or a 1-18C bivalent hydrocarbon group, X is 1 to 4, and M1 represents a metal of the Group VIIb or VIII in the Periodic Table or a compound of formula III wherein R7 represents a 1-18C bivalent hydrocarbon group and X and M1 are same as above), and an aniline polymer. Since the composition contains an aniline polymer, it has excellent electromagnetic wave shielding performance, is good in workability, and hardly sags. Therefore, it is suitable to be used at sites where conductivity is required particularly for the purpose of electromagnetic wave shielding, for example, in architecture and civil engineering.