Ultrathin polyimide fibers were prepared using the organoalkoxysilanes (3-triethoxysilylpropyl)succinic anhydride (TESP-SA) and (3-amino)propyl triethoxysilane (APTES). In the first step, a viscous solution of the corresponding poly(amic) acid (PAA) was produced and electrospun at various high voltages. The fiber diameter distributions of the as-prepared fibers were measured. The thermal imidization at 220 degrees C resulted in the formation of an organic-inorganic hybrid polyimide fiber assembly as shown by FTIR/ATR. Surface morphology was investigated by means of SEM images. TGA measurements made evident that the prepared fibers begin to decompose at 380 degrees C. XRPD pattern of the fibers revealed that a certain ladder-like order exists in the fibers. The water vapor absorption of the thermally (220 degrees C) treated ultrathin polyimide fibers was evaluated. The fiber assemblies treated at 110 degrees C were water soluble, whereas those treated at 220 degrees C were insoluble in water and organic solvents. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 1274-1281, 2013