Centrosema macrocarpum is a tropical legume well adapted to the Pucallpa ecosystem, but lack of information, especially conceming sowing rates and initial P fertilization are preventing its greater utilization as a cover or forage crop in the Peruvian tropics. This study was conducted to detemine optimum sowing rates and P fertilization levels for the establishment of C. macrocarpum. Three sowing rates (5, 10, and 15 kg seed per ha) and three P initial fertilization levels (O, 20, and 40 kg/ha) were tested from December 1997 to April 1998 using a Randomized Complete Block design, with a Split Plot experimetal layout on an acid, infertile Ultisol at the IVITA-Pucallpa Experimental Station. Response variables were plant density and cover at 4, 12, and 20 weeks after planting, and dry biomass at 12 and 20 weeks. Sowing rates significantly increased plant density (p<0.0001 ), but no differences were detected at each subsequent evaluation after planting. Plant numbers were not affected by the P fertilization level. Sowing rates and P levels, both individually (p<0.0001) and interactively (p<0.0001), significantly increased C. macrocarpum cover and dry biomass. The analysis of these responses to the combined effect of sowing rates and P levels at 20 weeks after planting suggests that legume covers of over 80% can be obtained with 5 kg of seed per ha and 20 kg/ha of P. If dry biomass is the response variable of choice, higher P levels ( 40 kg/ ha) and sowing rates (10 kg/ha) are recommended.