The present invention provides a method of demonstrating stain-proof efficacy of an oral care composition, comprising the steps:(a) sticking hydroxyapatite powder uniformly onto a substrate(b) immersing the substrate sticked with hydroxyapatite powder into a slurry or solution of the oral care composition(c) drying the immersed substrate and(d) contacting the dried substrate with a slurry or solution of stain to observe stains behavior.