Using enzymatic hydrolysate of corn gluten as a model solution, we measured the ultrafiltration permeate flux for periodically oscillating transmembrane pressure gradient. The objective was to evaluate the potential flux enhancement of the square-wave pressure oscillation, not pressure reversal. It was expected to instabilize the solute layer deposited on the membrane surface by repeatedly inducing its compression and relaxation. The oscillation was applied in the later part when the instantaneous flux dropped to a half of the initial flux. It was observed that the solute layer was more readily relaxed than compressed, which indicated that the time constant for the compression at higher pressure was larger than that of the relaxation. As a result, the time-averaged overall flux of the oscillatory-pressure filtration increased slightly (approx. 11 %) over the constant-pressure filtration.