Samples of PA-100 ultrafiltration membrane of the Mifil brand have been scanned with an AISTNT SmartSPM-1000 atomic force microscope, and the images have been processed using the program Gwyddion. The pore size distribution data have been subjected to statistical processing and interpretation. The fitting curves of distribution are proposed, with their accuracy having been estimated using the Pearson and Kolmogorov goodness-of-fit criteria. Good agreement of the results with the data obtained by a modified fluid squeezing method has been achieved. It has been shown that the pattern of the distribution curve remains the same for different parts of the membrane.