To obtain a composition which is durable and has an excellent antistatic property and a heat resistance by compounding as its main component a modified polyalkylene glycol compound having a specified number average molecular weight.

An antistatic agent comprises, as its main component, a modified polyalkylene glycol compound of formula I, which has a number average molecular weight of 4,500 to 30,000 and a Griffin's HLB value of 8 to 18, and an antistatic composition comprises a mixture of the antistatic agent and an organic metal sulfonate compound of formula II at a mixing ratio by weight of 90/10 to 55/45. If necessary, the composition may further comprise an antioxidant, a heat stabilizer, a UV absorber, a flame retardant and the like. When using a polyester resin, it is preferred that the antistatic agent is present in an amount 0.5 to 20 wt.% and, when the organic metal sulfonate is used in combination, its mixing amount is within a range of 0.1 to 10 wt.%, both based on the matrix polymer. In the formula, R1 represents a 4-6C alkylene; R2 represents an alkylene; n is 90 to 455; m and k are each 3 or over; R' represents a monovalent hydrocarbon; R" represents a 2-4C alkylene; and M represents an alkali metal such as Na, K, L or the like.