The growing interest in sustainable lignin valorization has prompted the exploration of new recovery methods compatible with modern kraft pulp mills. This study investigates the use of ultrafiltration for extracting lignin, referred to as oxlignin, from oxygen-delignification wash liquors. Unlike traditional acid precipitation, ultrafiltration enables lignin concentration and fractionation without disrupting the high-pH conditions required for brown stock washing or interfering with the sodium-sulfur balance of the recovery cycle. The oxlignin also has properties similar to lignosulfonates rather than kraft lignin. Using industrial process streams, ultrafiltration successfully prepared oxlignin, as confirmed by characteristic UV-vis absorbance features at 280 and 340 nm. These results demonstrate the ability to tailor lignin composition and open new opportunities for producing application-specific lignin products, such as dispersants or performance additives in bio-based materials. The retained filtrate could be suitable for reuse in the pulping process, ensuring integration with existing operations. Despite practical challenges such as membrane cost and fouling, the use of robust ceramic membranes offers a technically viable path forward for industrial implementation.