Objective To explore the effect of L-ascorbic acid(AA) for reducing the fibroblast cells induced by cobalt(co)cytotoxicity.Methods The experiment was divided into the blank control group,Co2+ group,Co2++AA group,cobalt nanoparticles(CoNPs) group,CoNPs+AA group and AA group.The AA pretreated for 1 h was performed in advance.The CCK8 assay was used to detect the CoNPs and Co2+ induced and AA-treated cytotoxicity.The fluorescence staining was used to measure the production of ROS in mitochondria.The real-time polymerase chain reaction(PCR) and Western blot were used to measure the expression of related protein and related molecular mRNA respectively.Moreover the cytochrome-C level in cytoplasml was detected.Results After treating the cells by CoNPs and Co2+,the cells appeared apoptosis.CoNPs could significantly induce ROS generation;the proapoptotic factors(caspases-3,and Bax) were significantly increased,while the anti-apoptotic factor Bcl-2 expression was decreased;cytochrome C and AIF expressions were up-regulated and released from mitochondria into the cytoplasm,after AA pretreatment,these changes caused by CoNPs were decreased.Conclusion AA can reduce the CoNPs caused cytotoxicity by reducing ROS generation and release,but can not weaken the Co2+ toxic effect.