To evaluate the antioxidation of dihydrobiopterin reductase and to explore the effect of A278C mutation of the quinoid dihydropteridine reductase (QDPR) gene on its antioxidant activity. First, plasmids with different genes (wild and mutant QDPR) were constructed. After gene sequencing, they were transfected into human kidney cells (HEK293T). Then, the intracellular production of reactive oxygen species (ROS) and tetrahydrobiopterin (BH4) was detected after cells were harvested. Activations of nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4), glutathione peroxidase 3 (GPX3), and superoxide dismutase 1 (SOD1) were analyzed to observe the oxidative stress after transfection. The expression of the neuronal nitric oxide synthase (nNOS) gene was analyzed by semiquantitative reverse-transcription polymerase chain reaction (RT-PCR). We also detected the activation of transforming growth factor beta 1 (TGF-beta 1) by enzyme-linked immunosorbent assay (ELISA) to observe the connection of TGF-beta 1 and oxidative stress. The exogenous wild-type QDPR significantly decreased the expression of nNOS, NOX4, and TGF-beta 1 and induced the expression of SOD1 and GPX3, but the mutated QDPR lost this function and resulted in excessive ROS production. Our data also suggested that the influence on the level of BH4 had no significant difference between mutated and the wild-type QDPR transfection. Wild-type QDPR played an important role in protecting against oxidative stress, but mutant QDPR failed to have these beneficial effects.