Oxidative stress is an important factor in the pathogenesis of insulin resistance (IR) in type 2 diabetes mellitus (T2DM). Bioactive peptides from nuts have been shown to alleviate oxidative stress and IR. However, the specific mechanisms underlying their activity remain unclear. This study investigated the protective effects of three novel peptides derived from Juglans mandshurica Maxim., LVRL, LRYL, and VLLALVLLR, against high glucose-induced IR and oxidative stress in HepG2 cells. The possible mechanisms underlying these effects were also elucidated. The walnut-derived peptides improved glucose consumption, glucose uptake, and glucose transporter type 4 (GLUT4) translocation, and elevated the phosphorylation of insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt). They also increased the activities of glutathione peroxidase (GSH-Px), catalase (CAT), and superoxide dismutase (SOD), the nuclear transport of nuclear factor E2-related factor 2 (Nrf2), and the protein expression of heme oxygenase-1 (HO-1). Furthermore, the walnut-derived peptides reduced high glucose-induced ROS overproduction and the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38. These results suggested that walnut-derived peptides protect HepG2 cells from high glucose-induced IR and oxidative stress by activating IRS-1/PI3 K/Akt and Nrf2/HO-1 signaling pathways.