Abstract: A new experimental design method named the step climbing method (SCM), as well as a new global criterion (NRC), are proposed for the selectivity optimization of thin layer chromatography. The method offers chromatographers a convenient means to decide the optimum developer composition for thin layer chromatography. The principle of the method is described, and examples of applications in pharmaceutical analysis are given to certify the feasibility of the method. Clearly, it may also be used for the selectivity optimization in high performance liquid chromatography.