The attractive features of nanomaterials enable them to be used in a variety of areas including drug delivery (DD) systems. The advantages like better targeting and effective delivery, promote the usage of these materials in the structure of DD. However, the hazardous effects of nanomaterials must be considered before allowing them to be utilized in vivo. Because of their metallic based natures and small dimensions, nanomaterials can be toxic to human beings. Therefore the cons and pros of the usage of nanomaterials in DD systems must be extensively considered. In this review, after the brief history of DD systems and the usage of nanomaterials in these systems were presented, the selected nanomaterials cons and pros towards DD were examined. In conclusions and feature perspective part, the inadequacy of numbers of in-vivo studies was discussed and the need for more in-vivo tests was emphasized.