Inorganic fiber sizing agent and inorganic fibers

An inorganic fiber sizing agent comprising an epoxy compound (A), an aliphatic sulfonic acid salt (B), and a nonionic surfactant (C), wherein taking the sum of the contents of the epoxy compound (A), the aliphatic sulfonic acid salt (B), and the nonionic surfactant (C) as 100 parts by mass, the inorganic fiber sizing agent contains the aliphatic sulfonic acid salt (B) at a content of greater than or equal to 0.01 parts by mass and less than or equal to 0.9 parts by mass, wherein the aliphatic sulfonic acid salt (B) is an aliphatic sulfonic acid alkali metal salt.