This study describes changes within the Leguminosae plant family along two to 25 years of secondary succession after slash-and-burn agriculture and compares regrowth with mature rain forest legume species composition. Research was conducted on a 21-site (12.9 ha) chronosequence and covered all legume plants > 50 cm height. Legume biomass shares ranged from 4–8% in secondary regrowth and were two to four times higher in mature rain forest (17%, or 78 tons ha⁻¹). Legume taxonomic composition differed strongly between secondary and mature rain forests, and floristic similarity (Jaccard's coefficient) of legumes between both forest types was only 34%. Successional changes in legume vegetation shares and taxonomic composition were weak within secondary regrowth, though repeated slash-and-burn did affect legume vegetation. Legume functional composition changed along succession with high shares of potentially N₂-fixing lianas in young regrowth. We conclude that 1) the composition of legume species in the community differs strongly between secondary and mature rain forest but legume composition along regrowth does not provide an adequate criterion for the definition of optimum fallow periods, and 2) legume lianas assume a key functional role in biological N₂-fixation and ecosystem N-cycling especially early along succession.