The Stylosanthes is a group of leguminous plants drought tolerant, with great adaptability to low soil fertility and association with nitrogen-fixing bacteria. Some are used as fodder and green fertilization. These are species with a wide distribution in tropical, subtropical and temperate in the Americas, tropical Africa and Southeast Asia. Stylosanthes capitata has rounded leaves, reaching up to one meter tall, while Stylosanthes viscosa are oblong leaves and the species reaches up to forty inches in height. Nitrogen is a macronutrient required in large quantities in the plant, and its availability limiting factor for growth. Leguminous plants have the ability to assimilate inorganic nitrogen environment (or ammonium nitrate) and synthesize all amino acids and proteins, and other nitrogenous organic compounds present therein, and in conditions of low availability of nitrogen in the environment fixing bacteria of the group Rhizobium sp. establish a symbiotic association with leguminous plants, infecting the root system forming root nodules. The experiment was conducted at the Federal University of Mato Grosso do Sul, Campus of Três Lagoas - MS, Brazil. The soluble protein content in the species S. viscosa and S. capitata was conducted at seven and two months after planting, respectively, according to Bradford’s method (1976), in a completely randomized design with 20 replications. S. capitata in the amount of protein found was about two times higher than S. viscosa and in consequence it is expected that the S. capitata contains a larger amount of amino acid incorporated in their leaves, even at the initial stage of its development. This result may have been influenced by the age of the plants, as young tissues have a high biosynthetic activity by increasing the production of various compounds including proteins.