Disclosed is a microemulsion for a fiber treating agent providing softness, hydrophilicity, improving texture of a fiber and stability and dilution ability. A microemulsion composition includes the following components (A) to (E): (A) a linear organopolysiloxane having two or more polyoxyalkylene-containing organic groups represented by —CH2—CH(OH)CH2O—(C2H4O)b—(C3H6O)c—Z per molecule and a viscosity at 25° C. of 100 to 5,000 mPa·s in an amount of 80-98 mass %, (B) a nonionic surfactant, with an HLB factor of 12-16, in an amount of 1-10 parts by mass, based on 100 parts by mass of the component (A), (C) an anionic surfactant in an amount of 0 to 3 parts by mass, based on 100 parts by mass of the component (A), (D) an organic acid in an amount of 0.5-2 parts by mass, based on 100 parts by mass of the component (A), and (E) water in an amount of 1-5 mass %.