The effects of Leech Salivary Extract (LSE) on some haematological, immunological and organ weight parameters in rats, during a twenty eight days oral administration of 25, 50 and 100 mg/kg body weight doses, was investigated. LD50 and sub chronic toxicity was determined using standard methods. The oral LD50 was above 5000mg/kgbw. Oral administration of LSE (25mg/kgbw, 50mg/kgbw, 100mg/kgbw) for 28days had no significant (p>0.05) effect on the differential white blood cells (lymphocytes, monocytes, basophils, neutrophils, eosinophils), red blood cell indices (RBC count, PCV, HB, platelets, MCHC and MCH), feed intake, body weight gain and relative organ weight of lung, heart, liver, kidney, spleen and stomach of rats. However, the LSE evoked a significant (p>0.05) increase in the level of MCV in treated rats compared to the control. These results, indicating low toxicity and no negative significant effects of LSE on haemato-immunological indices in rats, suggest that the extract is safe for development and use as therapeutic for managing clinical conditions.