PURPOSE: To obtain the titled rubber of outstanding processing workability, breaking strength and water resistance, suitable for electromagnetic shielding materials, etc., by incorporating conductive carbon black in a rubber component comprising organic rubber and specific polyorganosiloxane followed by crosslinking.

CONSTITUTION: The objective rubber with a volume resistivity 10-3W107Ω.cm can be obtained by incorporating (I) 100pts.wt. of a rubber composition comprising (A) an organic rubber with a Mooney viscosity ML1+4 20W160 (e.g. natural rubber) and (B) a polyorganosiloxane of formula (R and R' are each hydrocarbon substituent; n ≥3) with ≥6 (pref. 20W50)mol% of the substituents R and R' being such hydrocarbon group as to be ≥350 (pref ≥700) in the Small's molecular attraction force constant in a weight ratio (A)/(B)=95/5W0/100 (pref. 80/20W20/80) with (C) 5W200 (pref. 10W150)pts.wt. of conductive carbon black with an average particle size ≤1,000 followed by crosslinking.