In this study, the in vitro apparent rumen degradability of organic matter (ARDOM) and plant secondary metabolites (ARDPSM) of three tropical legumes (Mucuna pruriens, Canavalia ensiformis and Leucaena leucocephala) were assessed. For this, single end-point incubations (24 h) as well as kinetic assessments (0, 2, 4, 6, 8, 10, 12 and 24 h) were set up with different inocula sources, i.e. ruminal inocula from Belgian and Cuban sheep. L-mimosine, L-canavanine, Concanavaline A (Con A) and trypsin inhibitor (TI) were the plant secondary metabolites (PSM) targeted in this study. Bean and forage/bean meals of M. pruriens and C. ensiformis as well as their PSM were extensively degraded during 24 h incubation (0.70 and 0.78 g ARDOM/g of organic matter (OM), respectively and > 0.80 g/g for L-canavanine, > 0.76 TIU/TIU for TI and > 0.95 g/g for Con A, for both legumes). Forage meal of L. leucocephala was considerably less degraded, with apparent ruminal degradabilities of 0.20 and 0.35 g ARDOM/g OM after 24 h incubation with Belgian or Cuban sheep inoculum, respectively. This could -at least partially -be related to L-mimosine, present in L. leucocephala, which was hardly degraded in the Belgian incubation, while a more extensive ruminal breakdown was observed under the Cuban conditions (0.05 to 0.78 g ARDPSM/g PSM, respectively). The negative effect of L-mimosine on OM degradability was supported by in vitro incubations with straw and inoculum from Belgian sheep, as ruminal degradation of straw was 31% lower when L-mimosine was supplemented.