The heterocycle-containing aromatic polyamide fibers of the invention are excellent in balance among mechanical characteristics, particularly balance among a tensile strength, an initial modulus and a strength in the direction perpendicular to the fiber axis, exhibit a high strength holding ratio under heat and humidity, and are excellent in flame retardancy, bulletproofness and cutting resistance, as compared to conventional aromatic polyamide fibers, and therefore can be favorably used in fields where severe mechanical characteristics and stability to environmental variation. Accordingly, the heterocycle-containing aromatic polyamide fibers of the invention can be favorably used, for example, in fields including a protective equipment, such as a helmet, a bulletproof vest and the like, a chassis for an automobile, a ship and the like, an electric insulating material, such as a printed circuit board and the like, and other various fields.