Concentrations of serum glucose (SG) and urea (SU), milk lactose (ML) and urea (MU) and their relationships to dietary gross energy (GE) and crude protein (CP) were studied in 16 lactating ewes in Urmia, Iran. Ewes were aged 3 to 5 years and were bred in a closed pen. They were fed alfalfa hay, pasture grass, concentrate and corn silage. Each lactating ewe was nursing a single lamb. Five ml of blood from v. jugularis, 50 ml milk and 200 g feed mixture were collected at 15 day intervals up to 135 days (9 samples). Serum glucose and urea concentrations were evaluated using a spectrophotometer, milk lactose in Polarimeter, gross energy by calculation method and crude protein by Kjeldahl methods. The mean values for dietary GE, CP, SG, SU, MU and ML were 2.39 Mcal/kg/DM, 14.1% food/DM, 2.69, 4.65, 3.67 mmol/l and 4.8 mg/dl milk, respectively. Significant differences (P < 0.01) were found for serum and milk indicators during the milking periods among the sampling times. Serum urea and milk urea irregularly increased while serum glucose and milk lactose irregularly decreased. Positive correlations were found (P < 0.05) between SU/MU (r = 0.45), MU/GE (r = 0.75), MU/CP (r = 0.70) and SU/CP (r = 0.97). Negative correlations (P < 0.05) were found between MU/SG (r = -0.17), SU/ML (r = -0.20) and MU/ML (r = -0.24). Based on results, it is concluded that urea, glucose and lactose would be appropriate variables in the prediction of crude protein and gross energy concentration of diet in lactating ewes.