Forward osmosis (FO) has been considered a novel technology for desalination. However, one of the major problems is permeate flux decline by fouling. This paper investigates the mitigation of calcium sulfate (CaSO 4 ) and colloidal (particulate) fouling in FO process by application of ultrasound (and/or pressure). Saturated CaSO 4 solution of 2000mg/L and silica (SiO 2 ) colloid of 5000mg/L with average diameters of 10–20nm were used as a model scalant and a model colloidal foulant, respectively. The results showed that CaSO 4 scaling in FO was almost fully reversible. On the other hand, colloidal fouling caused more severe flux decline and was challenging to clean. The application of pressure (5bar) to feed side, increased the initial flux by approximately 20% but subsequently resulted in a higher flux decline. Combination of ultrasound and hydraulic pressure to the FO system showed promising result (a significant increase of permeate flux and lower flux decline by CaSO 4 scaling and colloidal fouling).