Current studies being undertaken on the genus Smilax L. in Thailand suggest that there are 29 species present in the country. Ongoing revisionary work, which includes comparison with the revision of Smilacaceae by Koyama (1975), and a new species description by Moore et al. (2008) has resolved the following: five species are reinstated, namely Smilax hemsleyana Craib, S. myrtillus A.DC., S. ocreata A.DC., S. pertenuis T.Koyama and S. synandra Gagnep., while Heterosmilax indica A.DC., S. siamensis T.Koyama and S. bracteata C.Presl subsp. verruculosa (Merr.) T.Koyama are respectively synonyms of S. sumatrensis (A.DC.) P.Li & C.X.Fu, S. prolifera Wall. ex Roxb., and S. aspericaulis Wall. ex A.DC. Heterosmilax polyandra Gagnep. and H. sumatrensis A.DC. are placed under the genus Smilax as S. polyandra (Gagnep.) P.Li & C.X.Fu, and S. sumatrensis. Smilax polyacantha Wall. ex Kunth is a new record to Thailand.