Present work aimed to study some immunological and biochemical effects of Clindamycin on broiler vaccinated against Newcastle virus. Three groups of one day old Hubbard chicks each of 50 birds were used in this study. Group (1) was control non treated group (CG). Group C20 and C40 were given Clindamycin (20mg/kg and 40mg/kg body. wt) respectively in drinking water at 14th, 15th and 16th days of age. All groups were routinely vaccinated against Newcastle virus at 7 and 18 day of age. On 25th day of age, blood samples were collected from ten birds of each group for immunological and biochemical tests. Five birds from each group were slaughtered at the same age then the lymphoid organs (thymus, bursa and spleen) were carefully separated & weighed and each organ relative weight was determined. Number of dead birds were recorded throughout the experiment period (45 day age). It was observed that administration of Clindamycin decreased the leukocytic count haemagglutination inhibition antibody titer (HI), total protein, globulin and the relative weight of bursa in C20 and C40. It did not induce any significant changes in the differential leukocytic count, liver and kidney function tests, spleen relative weight in C20 and C40. While, relative weight of thymus and body weight gain significantly decreased in C40 and non-significantly changed in C20. While, feed conversion rate significantly increased in C40 only. In addition, C20 and C40 had higher mortality rates than CG. Conclusion: Clindamycin administration suppresses the chicken's immune response to Newcastle disease virus vaccine.