Mineral deficiencies represent an important factor responsible for the low ruminant productivity in Brazil, and cause a decrease in growth rate and weight gain, low reproductive efficiency and low meat and milk production. Calcium is one of the minerals most studied in animal nutrition due to its great number of functions in animal metabolism. It is located in soft tissues and mainly in bones. Citrus pulp, Lucerne hay, limestone, oyster shell meal and dicalcium phosphate have been studied as low cost alternative Ca sources. Using the isotopic dilution technique, it is possible to obtain the true availability for this mineral. The aim of this experiment was to study the effect of different Ca sources on true Ca availability in sheep.