Here we report an oxidation-induced transformation of [Au23(S-c-C6H11)16]-TOA+ (S-c-C6H11: cyclohexanethiolate; TOA: tetraoctylammonium) to the [Au28(S-c-C6H11)20]0 nanocluster by H2O2 treatment under ambient conditions. This is the first example of oxidation-induced transformation of one stable size to another with atomic precision. The product was crystallized and analyzed by X-ray crystallography. Further insights into the transformation process were obtained by monitoring the process with optical spectroscopy and also by electrochemical analysis. This work adds a new dimension to the recently established transformation chemistry of nanoclusters that involves size and structure transformations.