In this paper, the effect of three synthetic jet pairs on the mixing between two fluid streams in a planar mixing channel is examined at a net How Reynolds number of 2. They are mounted transversely to the incoming flow and operated 180 degrees out The PLIF technique is used to provide a visual impression of the effect of synthetic jets on mixing as their operating condition varies, whereas PIV is used to provide the complementary information about the flow structures produced by the synthetic jets and their role in promoting mixing. Our experimental results demonstrate that this inline fluid mixer with a simple design produces an excellent mixing at low Reynolds numbers. It is found that such a good mixing is the result of a significantly increased interfacial area created by these synthetic jet pairs. Based on the degree of mixing deduced from the PLIF data at some distances downstream of the synthetic jets, a functional relationship between the synthetic jet actuation frequency and amplitude is also obtained. This functional relationship can be used for selecting the synthetic jet operating conditions to ensure a good mixing for a scaled version of this fluid mixer. (C) 2013 Elsevier Ltd. All rights reserved.