This experiment was conducted to investigate the effects of olive leaves (OL) in chicken experimentally infected with P. multocida and to determine the (MIC) of (OL) water extract against P. multocida. A total of 60 balady chicks one-month-old (SPF) were randomly assigned to 3 groups, control and two experimental groups (20 birds / each). Chicks of the experimental groups, group (II) and (III) were intramuscularly injected with 0.2 ml/ bird of 18 hrs. broth culture of P. multocida containing 3x108 CFU / ml. Birds of group (III) given ration containing olive leaves (5gm/kg of ration). Clinical signs, mortality rates, organ invasion, and some haemato-biochemical parameters were recorded. Blood samples were taken 3, 7 and 14 days post infection for determination of RBCs count, HB concentration, total and differential leucocytic count, serum AST, ALT, creatinine, urea, triglyceride and cholesterol levels. Results obtained showed that feeding with OL reduced signs of illness, decreased mortality rate and invasion of lung, liver and spleen with P. multocida, at the same time showed significant increase in RBCs count, HB concentration and significant reductions in blood levels of AST, ALT urea, and cholesterol. Also water extract of OL inhibited the growth of P. multocida at (MIC) 250 mg/ml. In conclusion, dietary supplementation with OL reduced bacterial invasion and improved the haematobiochemical parameter in broiler chickens.