Objective To investigate the expression and significance of nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) in maternal peripheral blood and placenta and reactive oxygen species (ROS) in placenta in pregnant women with preeclampsia.Methods Sixty pregnant women with preeclampsia who visited Xuzhou Maternal and Child Health Hospital Affiliated to Xuzhou Medical University from March 2021 to October 2022 were selected, including 30 early-onset (early-onset group) and 30 late-onset (late-onset group) cases. Another 30 healthy pregnant women in the hospital during the same period were selected as controls (normal group). The relative mRNA expressions of NOX2 in maternal peripheral blood and placental tissues and the relative mRNA expression of ROS in placental tissues of each group were detected.Results The positive expression rates and the relative mRNA expressions of NOX2 in maternal peripheral blood and placental tissues, and the positive expression rate of ROS in placental tissues in the early-onset group were higher than those in the control group and late-onset group (P < 0.05), while they were not different between the late-onset group and the control group (P > 0.05). Within the early-onset group, the level of NOX2 in peripheral blood of pregnant women no less than 30 years old was higher than that of those less than 30 years old (P < 0.05). There was no significant difference in the positive expression rates and the relative mRNA expressions of NOX2 in maternal peripheral blood and placental tissues, and the positive expression rate of ROS in placental tissues among patients with different body mass index, number of pregnancy and disease severity in the early-onset group (P > 0.05), and among patients with different age, body mass index, number of pregnancy and disease severity in the late-onset group (P > 0.05). In patients with preeclampsia, the level of NOX2 in maternal peripheral blood was positively correlated with the relative mRNA and protein expressions of NOX2 in placental tissues (r = 0.411 and 0.455, P =0.017 and 0.012), and the relative protein expression of NOX2 was positively correlated with the relative mRNA expression of NOX2 in placental tissues (r = 0.425, P =0.013). The positive expression rates of NOX2 and ROS in placental tissues in the early-onset group were higher than those in the late-onset group and the control group (P < 0.05).Conclusions The increased expression of NOX2 in peripheral blood and placenta and that of ROS in placenta may be related to the occurrence of early-onset preeclampsia. The pathogenesis of early- and late-onset preeclampsia could be distinctive.