Ethnopharmacological relevance: The American cockroach (Periplaneta americana L.) belongs to the family Blattidae, order Blattodea, and class Insecta. Its medicinal history in China spans thousands of years. In recent years, the anti-tumour activity of American cockroach has gradually attracted the attention of researchers and has a good application prospect in the treatment of tumours. Periplaneta americana has been found to contain proteins, peptides, amino acids and nucleosides. Pharmacological studies have shown that P. americana has anti-tumour, tissue repair, immunoregulatory and other activities. In this study, we investigated the chemical composition and mechanism of action of its active site against hepatocellular carcinoma. Materials and methods: We adopted ultra-performance liquid chromatography quadrupole Orbitrap high-resolution mass spectrometry (UPLC–Q-Orbitrap HRMS), measuring the accurate relative molecular mass, fragment ion peak, chromatographic retention time and reference substance information of the compound obtained by HRMS, to identify the chemical components of the anti-hepatocellular carcinoma (HCC) active site of P. americana based on data from relevant literature. We used western blotting (WB) to detect the expression levels of phosphoinositide 3-kinase (PI3K), phosphorylated protein kinase B (p-Akt) and Akt in the PI3K/Akt pathway and further study the molecular mechanism of the active site of P. americana against HCC. Results: UPLC–Q-Orbitrap HRMS identified 35 compounds from the active site of P. americana. Of these, 10 were amino acids, 1 was an alkaloid, 6 were nucleosides and their bases, 4 were dipeptides and cyclic dipeptides, 8 were organic acids, 2 were isoflavones and 4 were other compounds; 8 of these compounds were confirmed by comparison with the reference substance. The WB results showed that the relative expression levels of PI3K and p-Akt protein in the active site of P. americana in the medium-dose (concentration, 0.15624 mg⋅mL−1) and high-dose (concentration, 0.31250 mg⋅mL−1) experimental groups were significantly reduced compared with the blank control group (P < 0.05 or P < 0.01), whereas the expression level of Akt protein did not significantly change amongst the groups (P > 0.05). Conclusion: This study found that the anti-HCC active site of P. americana is composed of multiple components that can reduce the relative expression of PI3K and p-Akt protein. It exerts its anti-HCC effect by regulating the PI3K/Akt pathway. © 2021