An aromatic polymer containing aromatic polyamide structural units and aromatic carbohydrazide structural units at a specific ratio is disclosed. A film having a high Young's modulus, high elongation at break and low moisture absorption can be formed from such an aromatic polymer. Dehydration cyclization of a compound having a carbohydrazide structure can be conducted under mild conditions at low cost by causing the chemical reaction using a chemical which is selected from the acids and bases.