Tilapia could be one of important culture fish species and has important role in fisheries economics in the world. It was accepted as culture species in more 100 countries in the world in order to some specificity such as adaptation ability in new environment, rapid reproduction and suitable growth. Some important infectious diseases such as bacterial and viral diseases could be considered as one of important basic challenge in aquaculture development. Recent investigation on tilapia approved that after introduce of tilapia fry to culture ponds probability of infection to some bacterial and parasites (Monogenes and Protozoan) would be increased after short period. Also, Iridovirus infection could be caused of heavy mortality in early stages of tilapia culture. Furthermore, Flavobacterium columnare infection is a common pathogen in early stages. The most important threats of the mid and last stages of tilapia culture could be due to some bacterial pathogens such as streptococcal disease that killing big fish from 150 – 300 g onward, as the most important pathogen affecting the tilapia culture industry. Well-known species of Streptococcus consist of (S.dysgalacti), (S.iniae) and (S.agalactiae ) and could be produced some clinical signs such as septicemia, meningoencephalitis, loss of appetite, emaciation, lethargy, diffuse bleeding on skin and internal organs, exophthalmia, spiral swimming and heavy mortality in affected tilapia. Furthermore, viral diseases have more importance in tilapia culture and rate of morbidity and mortality were related to age, water temperature and other culture conditions. Some Herpes-like virus, Iridoviral disease (IVD) and Viral Nervous Necrosis (VNN) could be considered as most important viral threats in tilapia industry in the world.