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Background: The high ureolytic activity of rumen microbiota is a concern when urea is used in ruminant feed, because it leads to fast urea conversion, resulting in possible intoxication and lower nitrogen utilization. This study intended to microencapsulate urea using carnauba wax to obtain slow-release systems in the rumen. The experiment was conducted in a randomized block design, arranged in a 3 × 2 factorial, with the urea encapsulated with carnauba wax in ratios of 1 : 2; 1 : 3, and 1 : 4 (U ME 2; U ME 3, and U ME 4) and two particles sizes (small, P S ; and large, P L )., Results: All formulations showed excellent properties, including inhibition of urea hygroscopicity. The formulation U ME 2 exhibited the greatest yield (91.6%) and microencapsulation efficiency (99.6%) values, whereas the formulation U ME 4 presented the greatest thermal stability (259.5 °C) and lowest moisture content (1.81%). The U ME 2 formulation presented a slower release than the other U ME formulations studied., Conclusion: The production of urea microspheres using carnauba wax was successful for all microencapsulated systems developed, evidencing the promising potential for use in ruminant animal diets. The U ME 2 formulation with large particles is the most recommended because it permitted greater resistance to microbial attack, allowing a slower release of urea into the rumen, reducing the risk of intoxication or ruminal alkalosis. © 2018 Society of Chemical Industry., (© 2018 Society of Chemical Industry.)