Animal toxins have shown applicability in treatments of various diseases, here some investigations of scorpion and spider venom peptides as cancer treatments have been presented. Scorpion peptides are believed to have antitumor and analgesic effects and may present the potential to be applied in human medicine as a drug for cancer. Similarly, some spider peptides either directly or indirectly are also proved to regulate tumour cell growth and death. Mechanism involved includes promoting cell apoptosis to prevent translocation of cancer cells thus control tumour growth. Such effects make these peptides promising drug candidates for cancer treatment. All five of scorpion venom peptide drugs being approved by FDA for clinical treatment, from which remarkable treating outcomes have been observed when treating cancers. In this paper, general aspects of different scorpion venoms as well as their anticancer mechanism have been thoroughly analysed, from which the successful application of Buthus martensii Karsch analgesic peptide in treating carcinoma was elected as the representative case.