PURPOSE: To obtain a composition leading to computer housings, tanks, etc. which gives outstanding mechanical strength and electrical conductivity, by incorporating a synthetic resin with specific carbon fiber produced by vapor growth process and short fiber.

CONSTITUTION: The objective composition can be obtained by incorporating (A) a synthetic resin with (B) carbon fiber produced by vapor growth process, with a diameter of 0.01W3(pref. 0.05W0.5)μ and aspect ratio of 2W108 (pref. 20W1,000) and (C) short fiber. Said carbon fiber may have such amount of acidic functional group as to be 4W30μeq/m2 per surface area. The amounts of the components A, B and C to be blended are pref. such as follows (weight ratio): carbon fiber : short fiber : synthetic resin = 3W40:5W60:20W90.