The reactive oxygen species (ROS) can be generated by intake of environmental pollutants, smoke, tobacco, xenobiotic, drugs, medical materials, radiations, pesticides, industrial solvents and ozone. The processes running in the cell membranes, peroxisomes, mitochondria and endoplasmic reticulum also generate ROS. ROS can be activated by numerous external factors, and play an important role in cancer growth and metastasis. ROS and tumor cell interaction could activate the signalling pathways, promoting cell proliferation, invasion, inducing angiogenesis, inflammation and cellular transformation in cancer. A better understanding into the mechanism of ROS in cancer progression might be useful for the development of biomarkers and therapeutic strategies. The objective of this review was to summarize the roles of ROS in different stages of cancer, cell invasion, angiogenesis and metastasis.