In this work, aramid nanofibers were prepared under mild conditions and aramid nanofibers reinforced poly (vinyl alcohol) (ANFs/PVA) composite films in different ratios were fabricated. The microstructure, thermal, optical and mechanical behaviors of composite films were characterized by fourier infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), atomic force microscope (AFM), scanning electron microscope (SEM), electronic universal testing machine and optical transmittance/fog tester. The FTIR tests revealed hydrogen bonding interactions were presented between aramid nanofibers and PVA in the composite films, which will enhance the dispersion of aramid nanofibers in PVA matrix. Aramid nanofibers with diameters of 20-30 nm can be clearly observed by AFM and SEM, and their composite films with relatively flat surface were observed from SEM. According to the mechanical test and DSC characterization, when the mass fraction of aramid nanofibers was about 6.0%, both the mechanical and thermal performance of the composite films achieved the best.dispersion of aramid nanofibers in PVA matrix. Aramid nanofibers with diameters of 20-30 nm can be clearly observed by AFM and SEM, and their composite films with relatively flat surface were observed from SEM. According to the mechanical test and DSC characterization, when the mass fraction of aramid nanofibers was about 6.0 wt%, both the mechanical and thermal performance of the composite films achieved the best.