This paper reports a quantitative survey of the composition, diversity and structure of the plant communities on six islands of Uyuni and Coipasa salt lakes (Bolivia). Plant communities on each island were examined via the use of 10 transects, along which species richness and abundance were recorded. Seventy-one species were found in total, representing pteridophytes (6%), gymnosperms (1%), monocotyledons (14%) and dicotyledons (79%). About 21% of the species were endemic or faced some degree of threat. The calculation of Shannon-Wiener α-diversity indices and comparisons of community structure revealed similarities between the islands. Indeed these analyses suggest the existence of a single floral assemblage; however, small differences in the plant communities were visually identified during fieldwork. These islands are home to a considerable subset of the Altiplano’s flora and appear to have been little disturbed. They should therefore be the subject of surveillance/conservation programs.