During production and use of carbon nanomaterials, they are prone to enter the environment and ultimately the human body, and subsequently to pose a risk of adverse health effects. This work has for the first time found that epoxide is highly active to form ROS, possibly leading to a strong oxidation stress to humans, while carboxylation and hydroxylation have little influence on the oxidation potential. This suggests that more attention should be paid to epoxide-containing carbon nanomaterials.