Abstract: Surgical resection, radiotherapy, chemotherapy, and immunotherapy are the main therapies for cancers. These cancer therapies all prolong patient survival, but also bring multiple side effects. Gut microbiota participates in almost all the physiological and biochemical processes of the host, playing a key role in human health and diseases. As an exogenous intervention, probiotics can prevent diseases and enhance immunity. Their anti-cancer ability and ameliorative effect have received increasing recognition. Herein, we reported the latest findings on gut microbiota and cancer pathogenesis, focusing on the application of probiotics in reducing the side effects caused by cancer therapies and hoping to provide supportive references for the clinical use of probiotics in cancer treatment.