A composition for a highly reliable thermal interface materials includes: (A) moisture-resistant polymer with a water permeability coefficient preferably less than 10−11 cm3 (STP) cm/cm2 S Pa, (B) gas barrier polymer having oxygen permeability coefficient preferably less than 10−14 cm3 (STP) cm/cm2 S Pa, (C) antioxidant, (D) thermal conductive filler and (E) other additive or optional materials. The thermal interface materials placed in between the thermal generating and dissipating devices can effectively barrier water and oxygen penetration, preventing the thermal fillers from degradation and improving the reliability of the devices.