Cancer stem cells are believed to be responsible for the cancer-initiating step and resistance to chemotherapy drugs. Studies have shown that cancer stem cells are silent and have no metabolic activity. The main reasons behind tumors resistant to therapies are lack of activity of cancer stem cells and division of cancer cells. This cell population, like normal stem cells, is capable of self-renewing and responsible for survival of tumor and its genetic and metabolic differences. Cancer stem cells can undergo chemotherapy during the treatment, but, the incidence of secondary tumor occurs due to unequal division of cancer stem cells and new tumor cells grow that are multi resistant to chemotherapeutic agents. Therefore, identifying and characterizing cancer stem cell will lead to a better understanding of its controlling pathways and developing better diagnostic and therapeutic methodologies in basic and clinical cancer researches. In this review the role of cancer stem cells in development of cancer and their heterogenic properties in gene expression and metabolism of the tumor has discussed. Finally, new therapeutic strategies that are often based on the use of nanocarriers are presented.