Complement are group of serum proteins which can be activated by antigen-antibody complexes or other substances, which may result in lysis of a microbial target, or a variety of other biological effects important in both innate and adaptive immunity. The last several years have seen an enormous expansion of parallel research on bacteria and the complement system and acquaint the role of complement proteins in biological phenomena. This study sought to find out the in vitro examination of bactericidal action complement proteins derived from blood sera of a defined group of urban and slum people against Shigella flexneri generating a critical problem in modern medical therapy for bacterial infections. This comparative study showed the susceptibility of clinical isolates of Shigella flexneri to bactericidal action of complement proteins of both urban and slum people blood serum. However the slum people indicated more effective complement mediated killing in comparison to urban people.