Compared to other organisms, insects are found in all the world. The diversity and evolutional success of insects depend on its relation with useful microorganisms. These microorganisms are found mostly in the intestines and epidermis of the insect. A Cockroach is one of the most important medical insects. All of the species of this insect live in dirty environments especially sewers. There are two species of disease-causing cockroaches: the German cockroach (Blatella germanica) and American cockroach (Periplaneta americana). The study aims at defining the role of P. americana as a carrier of disease-causing bacteria by isolating and determining these microorganisms from the body of the cockroach. The study included (18) samples of P. americana. Each sample was autopsied to get external parts as well as the digestive channel. These specimens underwent a bacteriological study to isolate and diagnose the species of bacteria and which parts carry them. Isolation results showed the diagnosing of (22) isolates of about 13 different species of bacteria, (82%) of isolates came from the external parts of the insect while (18%) isolated from the digestive channel. Most isolates belong to the family Enterobacteriaceae in 68.18%. First place went to Serratia marcescens with 36.36% of the isolated species then Kluyvera intermedia 13.64% . As for the rest species, all shared a ratio of 4.55%.