Abstract: Sitophilus oryzae and Tribolium castaneum have been two types of the most widely distributed and destructive pests during storage. The yield and quality of agricultural products can be reduced significantly under the two pests, such as grains, medicinal herbs, dried fruits, and processed products. However, the commonly used chemical control has caused a series of health and pollution. It is urgent to find green prevention and control, environmentally sustainable, and effective alternatives. Among them, the plant essential oils can be expected to serve as the prevention and control of stored grain pests. This study aims to explore the biological activity of Camphora longepaniculata essential oil against Sitophilus oryzae and Tribolium castaneum. A systematic investigation was also made to determine the insect-repellent and insecticidal properties of the essential oil of Camphora longepaniculata on S. oryzae and T. castaneum. Gas chromatography-mass spectrometry was then used to identify its main components. An analysis was also made to clarify the effects of the C.longepaniculata essential oil and its primary components (α-terpineol and 1,8-cineole), together with the light fraction of essential oil processing residues on the two pests. Finally, the activities were evaluated on the antioxidant enzymes (peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT)), digestive enzymes (amylase (AMS), trypsin, and lipase), detoxifying enzymes (carboxylesterase (CES), multifunctional Oxidase (MFO), cytochromeP450 (CYP450), and glutathione S-transferase (GST)), as well as acetylcholinesterase (AChE) in the pests under the most effective essential oils at the varying time intervals and concentration gradients. The results showed that the crude oil extracted from the leaves of C. longepaniculata shared the relatively high contents of 1,8-cineole (60.13%) and α-terpineol (8.05%). The contact activity of α-terpineol against S. oryzae and T. castaneum was the most effective, with the LD₅₀ of 0.03 and 0.12 μg/cm², respectively, followed by the contact activity of 1,8-cineole against the two pests, with LD₅₀ of 0.22 and 0.18 μg/cm², respectively. There was no significant difference between the contact activity of C. longepaniculata crude oil and the light fraction of essential oil processing residues against the two stored grain pests. There was the same and highest fumigation activity of 1,8-cineole and α-terpineol against S. oryzae and T. castaneum. The fumigation activity LC₅₀ of 1,8-cineole against the two pests was 14.06 and 14.34 μg/L air, respectively, while the LC₅₀ of α-terpineol was 15.99 and 14.95 μg/L air, respectively. There was the most ineffective fumigation activity of C. longepaniculata residue oil. All four essential oils shared significant insect-repellent concentration- and time-dependent activities against S. oryzae. Among them, the α-terpineol was the most effective for repelling T. castaneum, while the 1,8-cineole showed the lowest repellent effect on T. castaneum. Treatment with the α-terpineol also significantly influenced the enzyme activities in the two insect pests, thus increasing the activities of POD, digestive enzymes, detoxification enzymes, and AChE at higher concentrations. While the activities of CAT and SOD were inhibited as well. The activity of GST, CYP450, and MFO increased with the treatment duration in both insects, whereas the activity of POD, AChE, AMS, lipase, CAT, and SOD in S. oryzae were changed irregularly, and the activity of CES and trypsin were inhibited. Furthermore, the AMS, CES, POD, AChE, and trypsin were activated in T. castaneum, while the SOD and CAT were inhibited. There was an effect of α-terpineol on the concentration, time, and species of insects. Drastic changes were found in the different types of enzyme activities in the two pests. Among the four essential oils, the α-terpineol exhibited the best insecticidal, fumigant, and repellent activity against S. oryzae and T. castaneum, which markedly inhibited or increased the activity of antioxidant, digestive, and detoxification enzymes in the two pests, thus disrupting their normal physiological metabolism and inducing toxicity. Therefore,α-terpineol has the potential to serve as a biological pesticide for the control of S. oryzae and T. castaneum. These findings can also provide a theoretical foundation for the environmentally friendly prevention of camphor essential oil from stored grain pests.