In this study, effects of dietary levels of sage (Salvia officinalis L.) oil on growth, haematological parameters were evaluated on tilapia (Oreochromis niloticus). For this experiment, 360 fish (11.81 +/- 0.02 g) were used. Fish were divided into four equal groups in three replicates and were fed with diets containing 0, 0.25, 0.5 and 1 % of sage oil for 30 days. The results showed that the haematological parameters (total red blood cell count, hemoglobin concentration, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, total white blood cell count and differential leukocyte counts) showed no significant (P>0.05) differences between the control and all other treatments. Feed intake, specific growth rate, weight gain and final weight were decreased significantly with the increase of sage oil levels in diets (P<0.05). There was no significant difference in hepatosomatic index (HIS), viscero somatic index (VSI) and condition factor (CF). The data of this study show that sage oil can be used to diets of tilapia up to 0.25% without any adverse effect on growth, feed utilization and haematological parameters.