Ultrafiltration (UF) of gelatin liquor from marine source (tuna skins) has been performed on a tubular mineral membrane of cut-off 10,000 Da. An attempt was made to concentrate the fish gelatin as well as to purify it by means of the diafiltration technique (DF). Primary experiments were devoted to optimise the UF performances as a function of the main adjustable parameters. The influence of pH, transmembrane pressure, recirculating velocity, and working temperature on both volumetric permeate fluxes and protein retention rates was successively examined. Under the appropriate operating conditions, it was shown that the used membrane can achieve the initial concentration step of the gelatin solutions up to 12 wt% with a protein yield as high as 0.98. In addition, continuous DF proved useful to reduce the salt content of the solutions at an average desalting speed of 185 g/h.m(2) with a few loss of protein in the permeate side.