The Rxp locus in soybean [Glycine max (L.) Merr.] that conditions reaction to bacterial pustule was mapped by simple sequence repeat (SSR) marker analysis. A population of 116 F4-derived lines from a cross between the resistant parent Young and the susceptible parent PI 416937 was used for mapping. The Rxp locus was mapped 3.9 cM from Satt372 and 12.4 cM from Satt014 on linkage group D2. Linkage associations were confirmed by identifying a close association between the SSR genotype at each locus identified as flanking Rxp and the bacterial pustule reaction of individual lines derived from a population different from the one used for mapping. A molecular pedigree analysis showed that bacterial pustule-resistant cultivars inherited the resistance gene rxp from the ancestral cultivar CNS based on their consistent genotypic pattern at flanking marker loci. Based on the results of the study, marker-assisted selection for rxp would be very effective.