Feed was withheld from 8 donkeys for 7 days with free access water. Blood samples were collected each morning prefasting, fasting and refeeding periods. Serum was prepared and serum constituent were determined. During fasting, serum G.O.T., G.P.T. and total proteins concentration were maintained at or near prefasting values while there is a fluctuation in serum glucose value during the fasting period. Serum phosphorus, calcium and alkaline phosphatase were significantly decrease whereas total lipids, urea nitrogen, total bilirubin were increased during fating period.