Composition of polymer solutions on electrospinning process is an important factor to control spinnability and diameter of nanofibers. The optimum electrospinning conditions on fiber morphology as a high-efficiency filter media were established by adjusting applied voltage, distance, feed rate and concentration of poly(amic acid) (PAA)-dimethylacetamide (DMAc)/acetone solutions. The average diameter of PAA nanofiber was 440 nm. Isothermal heat treatment of the PAA nanofiber mats was carried out using an electric oven (at 200 degrees C) for 10, 30, 60, 90, 120, 150, 180, 210, and 240 min, respectively. Imidization degree and the thermogravimetric property of PAA mats were confirmed by ATRFTIR and TGA measurement. Imidization of nanofiber mats occurred after 30 min of heat treatment. There was not significant variation of ATR-FTIR intensity after heat treatment longer than 30 min. Weight loss of the polyimide mats was negligible for 4 weeks incubation at 200 degrees C. Optimized conditions of electrospinning and isothermal heat treatment of nanofibrous poly(amic acid) mats might useful for fabrication of efficient polyimide non-wovens as a heat-resistance filter media.