Abstract: Color concentration detection is one of the main monitoring processes in textile industry. Highly sensitive sensors and less cumbersome procedure in monitoring color concentration are required. Potential for using fibre optics sensor in such measurement is promising because of its high sensitivity and fast response. In this study, concentration of Remazol Black B (RBB) dye solution was measured by using Mach-Zehnder interferometer (MZI) sensor with concatenating tapered multimode fibre (MMF) between two sections of single-mode fibre (SMF). The aim of this work is to study the interaction between the operating parameters, diameter of MMF and concentration of RBB dye solution. Central composite design (CCD) coupled with Response surface method (RSM) was applied to obtain optimum operating parameters for achieving well-responding operating variables, relative output intensity and wavelength shift. The proposed sensor was tested through additional experiments at optimum conditions (MMF with diameter of 19.5 µm; dye solution with concentration of 200ppm and corresponding wavelength of 1550nm). The difference between the experimental and modeled data was only less than 10% which showed good agreement between them. Knowledge of this optimization sensing conditions, it may be useful and attractive to detect the concentrations of many other chemical compounds in practical applications.