The laminar flow diffusion interface control method was introduced in this paper. The method aimed at the control of the interface position and diffusion zone width of two co-flowing liquids in a microchannel. It consisted of a trial-and-error process and the Raman measurement. The method enabled the interface control when the control process is accompanied by diffusion, and does not require the information of liquid properties in the trial-and-error control process. The Raman microscope measured the local concentrations of liquid samples, so that the entire process was labeling-free. The reliability of the control method depends on the accuracy of the Raman measurement. Two prominent problems affecting the accuracy were dealt with. First, the microchannel cross-sectional configuration was optimized to guarantee the uniform concentration field in the Raman laser focus. Second, the laser-induced heating was eliminated by simply coating an aluminum film on the channel bottom. Eventually, this control method was proved to be convenient and effective. It can facilitate the sample preparation in a single microfluidic chip. (c) 2012 Elsevier B.V. All rights reserved.