Objective: To determine the diet of the bighorn sheep and identify differences in its composition between sexes and periods (reproductive and segregation). Design/methodology/approach: The study was conducted at the UMA Rancho Noche Buena, Hermosillo, Sonora, Mexico. To determine the plant species in the bighorn sheep feces the micro histological technique and a cell catalog of plants from the study area were used. From the diet information, the relative frequency, the Shannon-Weaver diversity index and the Kulczynski similarity index by sex and period (reproductive and segregation) were determined. Results: The diet of the bighorn sheep included 40 plant species, being herbaceous (36.14.4%) and grasses (26.88.9%) the most common. The male diet during the segregation period was mainly composed of grasses (36.2%) and female diet by herbaceous (30%) and grasses (29.8%). There were no differences in the diversity of the diets in males and females during the segregation period (H ́1.0), overall, their diets were very similar (80%). Limitations/implications: Collect a greater number of fecal samples by sex and period (reproductive and segregation) and to analyze the nutritional content of the plants consumed by bighorn sheep. Findings/conclusions: In this study, the sexual segregation exhibited by the bighorn sheep was not due to food preferences