Hierarchical micro/nanofibrous filters are fabricated by blending electrospun polyurethane (PU) nanofiber with polyethylene terephthalate (PET) microfibers followed by spunlace reinforcement. PET microfibers mainly act as a skeletal framework and PU nanofiber is employed for capturing fine particles. The incorporation of PU nanofiber optimizes inner structures and improves filtration properties of hybrid filters. The mean pore size decreases and pore size distribution shifts to smaller pore sizes with the increased content of PU nanofiber. When the PU nanofiber accounts for 1.87%, the composite filter exhibits a high filtration efficiency (76.63%) for PM0.26 and low pressure drop (173 Pa) under an airflow velocity of 53 cm/s. This composite filter exhibits a high quality factor of 0.084 Pa-1. Furthermore, the removal efficiency for PM2.5 reaches to 99.93% with a low terminal pressure drop of 263 Pa. The composite filters with excellent filtration performances prepared can be applied to industrial production and commercial applications. (C) 2019 Elsevier B.V. All rights reserved.