Lateral root (LR) formation is critical for plant growth. ROS (reactive oxygen species), especially hydrogen peroxide, play important role in LR formation. While the role of superoxide anion in primordia in LR formation is still unclear. Cerium oxide nanoparticles (nanoceria), as a potent ROS scavenger, are widely used in plants in terms of maintaining ROS homeostasis to improve stress tolerance. Whether ROS scavenging nanomaterials can promote LR formation or not and how to use ROS scavenging nanomaterials to study the role of ROS in LR formation remain unclear. In this study, we investigated the effects of three types of nanoceria—poly (acrylic acid) nanoceria (PNC, 6.5 nm, -36 mV), aminated nanoceria (ANC, 6.9 nm, 30 mV), and bulk nanoceria (BNC, 84.9 nm, -5.5 mV)—on LR development in Arabidopsis. Only PNC promoted LR formation, increasing LR numbers by 73.5%. Compared to control plants, PNC-treated Arabidopsis showed reduction in root H 2O 2 levels (up to 90.44%), alongside decreasing in superoxide anions (O 2 .─) and the changes of O 2 .─ distribution in LR primordia (LRP). Furthermore, DPI (diphenyleneiodonium, O 2 .─ inhibitor) treatment decreased LR numbers by 18.9%, while PNC treatment reversed this inhibition (12.25 ± 0.53 vs 8.38 ± 0.52). Transcriptome analysis revealed that PNC promoted LR development in Arabidopsis by modulating ROS metabolism and homeostasis, primarily through the regulation of ROS-related genes such as peroxiredoxins, peroxidases, and glutathione transferases. Interestingly, PNC treatment did not affect auxin distribution in Arabidopsis roots, as confirmed by DR5pro::GFP transgenic lines. Additionally, PNC did not alleviate the inhibition of LR formation caused by NPA (N-1-naphthylphthalamic acid, an auxin transport inhibitor). These findings suggest that PNC enhances LR formation through ROS modulation rather than auxin signaling.