This specification relates to a sliding material and a heat resistant filament which primarily comprises a liquid crystal polyimide, a liquid crystal polyamide or a liquid crystal polyamide-imide copolymer having at least one recurring structural unit selected from the formula (1) and the formula (2) and is excellent in heat resistance, mechanical characteristics and other fundamental properties of polyimides, and relates to significant improvement of heat-resistance by heat-treating the sliding material, the filament and the molded items. The liquid crystal polyamide-imide copolymer which comprises in a polymer molecule 0.05∼0.95 mole ratio of the recurring structural units of the formula (1) and 0.95 ∼0.05 mole ratio of recurring structural units of the formula (2) has excellent processing ability.