Protein nutrition plays a key role in ruminant performance and represents the largest proportion of costs in animal feed. The present study evaluated whether the roughage portion of Santa Inês sheep diets could be supplemented with different ratios of tropical kudzu as a protein source and assessed the best inclusion level of tropical kudzu based on digestibility, intake, nitrogen balance and feeding behavior. Twenty rams were evaluated during the 20-day experimental period, and they were fed formulated diets with a roughage portion (60%) consisting of Elephant grass and tropical kudzu, the latter supplemented at different concentrations (0, 25, 50 and 75% on a dry matter basis). Forty percent of the concentrate portion consisted primarily of ground corn and soybean meal adjusted to obtain an isoproteic diet. Chemical and bromatological analyses, as well as, analyses to assess intake, digestibility, nitrogen balance and feeding behavior, were conducted. No statistically significant differences were found (P>0.05) for the intake and digestibility of dry matter (DM), crude protein (CP), ether extract (EE), neutral detergent fiber (NDF), hemicellulose (HEMI), non-fiber carbohydrates (NFC) and total digestible nutrients (TDN) or for the feeding behavior (feeding, rumination and idle times in h/day) and nitrogen balance between the diets studied. Thus, tropical kudzu can be considered a feed alternative to supplementation with prime protein foods (in this case, soybean meal) in sheep diets.