This study was designed to investigate the effect of an extract of Nigella sativa L. on the heart rate and some haematological values in alloxan-induced diabetic rabbits. Fifteen New Zealand male rabbits were divided into three experimental groups: control, diabetic and N. sativa L.-treated diabetic. At the end of the experimental period (2 months), animals in all three groups were fasted for 12 hours and blood samples were taken for the determination of glucose levels, RBC and WBC (red and white blood cell) counts, packed cell volume (PCV), and haemoglobin (Hb) concentration. Heart rates were also measured by a direct-writing electrocardiograph before the blood withdrawals. It was found that N. sativa L. treatment increased the lowered RBC and WBC counts, PCV and neutrophil percentage in diabetic rabbits. However, the WBC count of the X sativa L. treated diabetic group was still lower than the control. N. sativa L. treatment also decreased the elevated heart rate and glucose concentration of diabetic rabbits. It is concluded that oral X sativa L. treatment might decrease the diabetes-induced disturbances of heart rate and some haematological parameters of alloxan-induced diabetic rabbits.