Cultivated potato (Solanum tuberosum) is susceptible to many pests and pathogens, but the most important threat to potato production is, so far, the late blight disease, caused by the oomycete Phytophthora infestans. Resistance genes from the wild Solanum sp. have been used by breeders to develop late-blight-resistant cultivars. Two sets of Black differentials potato genotypes (R1, R2, …, R11) were used to identify a new marker for resistance gene R11 of potato to late blight. RAPD polymorphic bands were isolated, cloned, and converted into SCAR primers. By amplification of genomic DNA with SCAR primers followed by enzymatic digestion with HinfI restriction enzyme, and verified by Southern blotting, a marker of R11 resistance gene of potato to Phytophthora infestans was identified.