Premise of the study:Polymorphic microsatellite markers were developed for Smilax sieboldii (Smilacaceae), a member of the S. hispida group with a biogeographic disjunction between eastern Asia and North America, to study the phylogeography and incipient speciation of this species and its close relatives.Methods and Results:Transcriptome sequencing produced 47,628 unigenes. Seventeen loci were developed from 122 randomly selected primer pairs. Polymorphism and genetic variation were evaluated for 68 accessions representing five populations of S. sieboldii. The number of alleles per locus ranged from four to 18; the expected heterozygosity ranged from 0.59 to 0.92. Twelve loci were successfully amplified in five related species: S. scobinicaulis, S. californica, S. hispida, S. moranensis, and S. jalapensis.Conclusions:These novel expressed sequence tag–derived microsatellite markers will facilitate further population genetic research of S. sieboldii and its close allies of the S. hispida group.