Formed-in-place (FIP) ultrafiltration (UF) membranes were formed from dilute solutions of chitosans with different molecular weights in 1% acetic acid on a macroporous titanium dioxide substrate. The ultrafiltration properties were characterized by investigating the rejection and permeability of a 1.0 g/L bovine serum albumin (BSA) solution at various pH and ionic strength conditions. The membrane stability to the crossflow shear and to the ionic strength was investigated. There was very little dependence of the membrane-formation capability and the membrane properties on the chitosan molecular weight. In contrast, pH had a marked effect on membrane surface properties, membrane stability, and membrane morphology.