Archaeological investigations of the lower Pleistocene deposits at Dmanisi (Lesser Caucasus, Georgia) have yielded an assemblage of hominin and faunal remains within a well-dated context. Although abundant vertebrate fossils have been recovered, paleobotanical studies have been limited. To address this, phytolith analysis has been conducted on two sections in order to reconstruct the distribution and evolution of vegetation throughout the entire sedimentary sequence. Large concentrations of phytoliths were recovered and analysed, permitting the reconstruction of climatic indices. The environmental data obtained from these phytolith assemblages are consistent with other palaeoecological data (i.e. geological, faunal and other archaeobotanical records). When considered together, they indicate an environment in which grasses were well-represented. In addition, the climatically important water stress indices derived from Dmanisi's phytolith assemblages suggest a period of increased aridity in the middle part of the stratigraphic sequence, which is contemporaneous with human occupations of the site.