For decades, researchers have tried to develop non-invasive mechanisms for monitoring of pathological conditions within the body of patients. Emerging nanotechnology enabled us to reach this aim. Scale of nano has the potential to increase early detection of pathological conditions from abnormal cells before diseased tissue or tumors development, can be considerable help to treat the diseases. In the recent years, “theranostics” has been emerged as a novel nano approach, which perform diagnostic detection, therapy and follow up, simultaneously. Therefore, theranostics can be considered as an appropriate therapeutic approach for personalized medicine, pharmacogenomics and molecular imaging which can develop novel therapies. Additionally, with a deeper molecular understanding, choosing drugs that are more effective will be possible. Finally, researchers believe that theranostics has the potential to monitor treatments with increasing drug effectiveness and prevention from inappropriate treats will reduce the cost of national health, significantly. In this survey, structure and some applications of theranostics and nano drug delivery systems have been evaluated, briefly.