In the present work, heat-endurable polyimide nanofibrous membrane-coated commercial polyimide nonwoven fabrics were prepared by electrospinning synthesized polyamic acid solution on polyimide mats followed by a thermal imidization process. Polyimide synthesized was confirmed by Fourier-transform infrared spectroscopy and thermogravimetric analysis tests. A higher viscosity of precursor solution resulted in a nanofibrous network coated on the nonwoven fabrics. The coated filter showed lower dimension of pores and greater portion of small pores. The proportion of pores less than 10 mu m reached as high as 71.2%. PM2.5 removal efficiency was increased from 81.4 to 97.2%. However, the pressure drop of air flow over the filters did not show significant changes. It suggested a facile method to improve the filtration performance of commercial polyimide nonwoven fabric filters.