This paper presents a numerical study of the effect of oscillation amplitude in oscillatory baffled column (OBC) using computational fluid dynamics. The numerical work was carried out for single phase liquid flow for an unsteady 3-D model using commercial software, Fluent (2006). This work was concentrated on the effect of oscillation amplitude. Three amplitudes of 5, 10 and 15 mm with constant frequency of 1 Hz are applied. Vortex and cycle average velocities at different points are analyzed. The studies show the maximum velocity for 5 mm, 10 mm and 15 mm in an OBC are 0.11 m/s, 0.25 m/s and 0.40 m/s respectively in the first cycle of oscillation. At a constant frequency, greater oscillation amplitude displaces the liquid to a further distance and builds a larger vortex. Vortex length was 1.5 times bigger when oscillation amplitude changes from 5 mm to 10 mm and 2 times when the amplitude is triple from 5 mm. The detailed validation is presented somewhere else; this research is focused on the effect of oscillation. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.