Abstract: Ruminant production in sub-Saharan Africa countries including Rwanda is predominantly based on natural pastures as well as crop residues. The quantity and quality of these feed resources vary with season, herbage type and geographical location. A study aiming at comparison of nutritive values and in vitro digestibility characteristics of four forage legumes used by farmers in two different agro-ecological zones was conducted. Samples of forage legumes from High (HA) and Middle Altitudes (MA) of Rwanda were randomly collected. Samples were oven dried at 60°C for 48 h and Dry Matter (DM) was calculated. Dried samples were proximately analysed for ash, Crude Protein (CP), Phosphorus (P) and Calcium (Ca). In vitro fermentation medium consisted of 1:2 ruminal fluid: McDougall's buffer and the experiment was a completely randomised design. Each sample (0.2 g, DM basis) was put in a gas syringe in three replicates per forage species sample. Syringes containing samples with 30 mL of fermentation medium and 2 blanks were incubated in a water bath at 39°C for 72 h. Data for in vitro gas production: (Metabolisable Energy (ME), Organic Matter Digestibility (OMD) and kinetic coefficients of fermentation were statistically analysed using PROC Nonlinear Model of SAS (9.3. Inc). Results showed that the nutritive values of four forage legumes from two agro-ecological zones (high and middle altitude) were highly significant difference (p<0.01). The CP of Medicago sativa (26.20%) and Mucuna pruriens (25.19%) from high altitude were higher than that of Medicago sativa (24.37%) and Mucuna pruriens (20.94%) from middle altitude while the CP of Stylosanthes scabra (15.73%) from middle altitude was higher than that of Stylosanthes scabra (12.76%) from high altitude. However, there was no significant difference (p>0.05) between Desmodium intortum from both sites (13.99 vs. 12.41%). Furthermore, there were no significant difference (p>0.05) of Ca and P content in forage legumes from high and middle altitudes. In vitro gas produced within 72 h, showed that forage legumes from middle altitude produced more gas than those of high altitude. The OMD and ME of forage legume from middle altitude were higher than those of high altitude. However, the Digestible Crude Protein (DCP) of M. pruriens and M. sativa from high altitude were higher than that of M. pruriens and M. sativa from middle altitude. The evaluation of ecological environment of forage quality, especially potential degradable portion showed that the indicative of better quality forages from warmer environment was higher than those of cooler environment of Rwanda.