In this paper a Monte Carlo Markov Chain (MCMC) method for resolving DNA mixtures containing at most four peaks per locus into a major and a minor contributor is presented. Unlike previous methods, this method can provide posterior probability assessments of the most probable genotype and a likely range for the mixing proportion. The proposed method is applied to two DNA mixtures where the true genotypes of the contributors are known. The method provides posterior probabilities of the genotypes of the contributes which concord strongly with the known facts.