Background: Blastocystis sp. Is a common intestinal parasites that known to have a crucial role in the pathogenesis of cancer via promoting the oxidative stress pathway. Colorectal cancer (CRC) is the second leading cause of cancer deaths worldwide. Objectives: we aimed to prove the carcinogenic effect of Blastocystis sp on oxidative stress status in vivo mice model. Methods: three groups of mice were infected with Blastocystis spp. isolated from CRC patients, symptomatic and asymptomatic infected patients. Nitric oxide (NO) and Glutathione peroxidase (GSH) levels were measured in plasma two weeks post-infection using biochemical assays. Results: High levels of NO and GSH were observed in infected mice that were infected with Blastocystis sp. Isolated from CRC patients in comparison to those that infected with Blastocystis sp. Isolated from patients with intestinal Blastocystis. Conclusion: our study supports the evidence that Blastocystis sp. enhances carcinogenesis by promoting oxidative stress damage in Blastocystis sp. infected mice.