Abstract: According to the invention, by preparing a solution of an aromatic copolyamide obtained by copolymerization of a specific third component, a spinning solution is stabilized even without using an alkali metal salt and a uniform aromatic copolyamide nanofiber can be obtained stably by an electrospinning method. Further, according to the invention, a fiber structure obtaining laminating a salt-free aromatic copolyamide nanofiber can be stably formed. Therefore, it can be applied to a product having no preference for ionic contamination of an alkali metal salt or the like, for example, a filter for gas or liquid filtration or an electronic component separator, and is useful in the textile industry.