The focus of this research was to evaluate plant density and dry matter yield of 'Ubon Stylo' {Stylosanthes guianensis) (95% germination) at seeding rates of 5, 10, 15, and 20 kg/ha. 'Ubon Stylo' was planted in August 2007 at the Isabela Substation of the Agricultural Experimental Station, University of Puerto Rico. The aftermath (first harvest) was 100 days after establishment. The experimental design was a complete randomized block with four replicates for the seeding rates. Variables assessed were: 1) Ubon Stylo and weed density (number of emerged plants in 1 m2) and dry matter yield (DMY; kg/ha). There were significant differences (p<0.05) between plant density of Ubon Stylo and weed species. Ubon Stylo plant density averaged 82 plants/m2 determined at the highest seeding rate (20 kg/ha). There was significant difference in DMY among seeding rates. Lowest DMY yield was observed at low seeding rate of 5 kg/ha (2758 kg/ha), but no difference was observed between the 10 (5,200 kg/ha) and 15 kg/ha (4752). Planting at a high rate 20 kg/ha (6100 kg/ha), although statistically significant from other rates, does not justify seed costs. It is concluded that seeding rates of Ubon Stylo between 10 and 15 kg/ha provides adequate plant densities and excellent DMY.