The structure and morphology of self-sustained electrospun nanofibrous membranes (ENMs) are key factors determining membrane performance for filtration applications. In this study, heat post-treatment (HPT) method was applied to modify the structural and morphological properties of polysulfone (PSU) ENMs, to improve their filtration performance and to obtain membranes suitable for wastewater treatment. The influence of the HPT temperature and time on the morphological structure of the PSU ENMs as well as on fouling and filtration performance was investigated. Microfiltration (MF) tests were conducted using humic acid model solutions with a concentration of 15 mg/L at pH 11. Increasing the HPT temperature or time, led to an increase of the mean nanofiber diameter along with a decrease of the mean size of the inter-fiber space, the void volume fraction and the water contact angle of the membranes. ENMs treated with a higher HPT temperature and a longer time exhibited higher nanofibers interconnectivity and a more compact structure with a smaller size of inter-fiber spaces. Under the same MF operating conditions, a commercial polyethersulfone (PES) MF membrane (HPWP, Millipore) had lower filtration performance (i.e. lower performance index, PI, 82 kg/m(2) h) than the treated-optimized PSU ENMs (i.e. 147 and 133 kg/m2 h for ENMs 9 and 10, respectively). The obtained results confirm the good performance of the developed PSU ENMs for MF applications.