Abstract: A study was conducted to compare the serum concentrations of glucose, Beta-hydroxybutyric acid, blood urea nitrogen and calcium in the prepartum and postpartum periods. One hundrad and thirty four blood samples were taken from native ewes in 2 periods (prepartum and postpartum) randomly in Tabriz area in Iran. The levels of glucose, Beta Hydroxybutyric Acid (BHBA), urea and calcium in blood were measured by spectrophotometer. The mean level of BHBA in prepartum period was higher than postpartum period significantly (p<0.05). The mean level of glucose in prepartum period was lower than postpartum period significantly (p<0.05).There was negative and significant correlations between BHBA and glucose levels in serum in prepartum and postpartum periods (r = - 0.55, p<0.01 and r = - 0.59, p<0.01, respectively). The level of BUN in prepartum period was greater than postpartum period but there was not significant. The level of calcium concentration in serum in prepartum period was higher than postpartum period significantly (p<0.01) but there was no significant correlation between glucose and calcium levels in serum in two periods. If concentration of BHBA in serum of pregnant ewes is being over 0.7 mmol L ¹ which were considered as sub clinical pregnancy toxemia. Twenty ewes (14.9%) suffered from it, that its occurrence was significant (p<0.05). It is concluded that hypoglycemia, uremia and hyperketonaemia in late pregnancy could be considered as sub clinical pregnancy toxemia. that should be considered in order to support prevention.