We present an optical-based, rapid method for the in situ porosity measurement of membranes through the electrospinning process. The method was developed by combining an optical method with in situ monitoring of the porosity of the electrospun membranes based on the measured reflected power density. The results showed that the area of bright and dark ratio is consistently proportional to the porosity of the electrospun membranes, which can potentially be used for actual characterization of the membranes. In addition, the effect of different incident angles of a laser beam was performed and compared. The porosity ratio of the electrospun membranes can be empirically evaluated as the determination coefficient R-2 = 0.9945 to 0.9876 can be obtained. The proposed method is successfully demonstrated and validated by the SEM images of the binary method. The potential applications include the in situ monitoring of the electrospinning process for the bioassembly and biomimicking of a human tissue with a great accuracy. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)