Common buckwheat, Fagopyrum esculentum, is a heteromorphic sporophytic self-incompatibility species while an annual wild species, F. homotropicum, is homomorphic self-cornpatible. An F₂ population was generated from an interspecific hybrid between them and used to determine the genetic basis of self-compatibility due to homomorphic phenotype. Homostyly appears to be controlled by a single dominant gene (designated “Ho”) as F₂ progenies segregated in a 3 homomorpic : 1 heteromorphic flower types. We used RAPD and bulked segregant analysis to identify three markers, OPB14₁₂₅₀, OPP8₁₀₀₀ and OPQ7₈₀₀, Iinked to the Ho gene. All three markers were mapped to the same side of the Ho gene with OPB14₁₂₅₀ being the closest at 0.6 cM. The mapping of this gene represents a first step toward better understanding of sexual reproduction system in buckwheat. These markers should be useful for marker-assisted selection for introgression of self-compatibility into common buckwheat.