Supplementing low-quality straw with protein meal, fresh tropical grass or legume forage improves dry matter intake (DMI), digestion and live weight gain in cattle (Doyle et al., 1986). Smallholder cattle farmers in Cambodia mostly use rice ('Oryza sativa') straw as a basal diet, especially during feed shortages. Supplementation of such diets with C4 grasses such as Mulato II hybrid ('Brachiaria' spp.) increases the intake and digestibility of rice straw, but mixed diets of grass and rice straw may still be deficient in rumen degradable N (RDN), especially if the grass is mature when cut. Inclusion of a tropical legume such as Stylo CIAT 184 ('Stylosanthes guianensis') as a source of RDN may further increase microbial activity and DMI. Our objective was to measure the effect of adding Stylo 184 forage to a mixed diet of rice straw and C4 grass fed to cattle in terms of DMI, digestibility, microbial crude protein (MCP) production and live weight gain.