In recent years, atomic layer deposition (ALD) has emerged as a powerful technique for polymeric membrane surface modification. In this research, we study Al 2 O 3 growth via ALD on two polymeric phase-inverted membranes: polyacrylonitrile (PAN) and polyetherimide (PEI). We demonstrate that Al 2 O 3 can easily be grown on both membranes with as little as 10 ALD cycles. We investigate the formation of Al 2 O 3 layer gradient through the depth of the membranes using high-resolution transmission electron microscopy and elemental analysis, showing that at short exposure times, Al 2 O 3 accumulates at the top of the membrane, reducing pore size and creating a strong growth gradient, while at long exposure time, more homogeneous growth occurs. This detailed characterization creates the knowledge necessary for controlling the deposition gradient and achieving an efficient growth with minimum pore clogging. By tuning the Al 2 O 3 exposure time and cycles, we demonstrate control over the Al 2 O 3 depth gradient and membranes' pore size, hydrophilicity, and permeability. The oil antifouling performance of membranes is investigated using in situ confocal imaging during flow. This characterization technique reveals that Al 2 O 3 surface modification reduces oil droplet surface coverage.