Membrane fouling is universally accepted as one of the critical problems limiting the wider application of membranes in liquid-solid separation. The in-situ ultrasonic application is one of the promising methods for reducing the extent of concentration polarization and increasing permeate flux during the membrane separation. A study was conducted to investigate flux behavior during a cross-flow ultrafiltration (UF) process to concentrate natural rubber skim latex, with in-situ sonication. Tubular polyvinylidine fluoride (PVDF) membranes with 200 kD molecular weight cut-off (MWCO) were selected for this Study. Experiments were conducted to Study the effect of skim latex preservation level with and Without sonication at a transmernbrane pressure (TMP) of 2 bar. Results showed the permeate flux remained constant with sonication, and a decline in flux was observed without sonication. This study was also able to determine the ideal preservation level where the in-situ sonication improved the permeate flux without affecting the stability of the feed. This ideal preservation becomes the optimum preservation level required for skim latex recovery by Ultrafiltration with in-situ sonication. The study also showed that an intermittent ultrasonic application with sonication ratio of I was comparable to that of continuous sonication.