Targeting innate immunity holds promise in cancer immunotherapy, particularly in improving checkpoint inhibitors. However, the use of agonists of the promising innate receptors TLRs and STING1-4 is facing challenges. Here we examined the antitumour function of the α-kinase 1 (ALPK1) receptor for bacterial ADP-heptose (ADP-Hep)5-7. Treatment of mice with ADP-Hep induced multiple proinflammatory factors including CXCL10 and CCL2, and stimulated Alpk1-dependent antitumour immunity. Mice bearing a gain-of-function ALPK1(T237M) disease variant8 also rejected grafted tumours. Using medicinal chemistry, we identified a more potent analogue, UDSP-Hep. In contrast to ADP-Hep, UDSP-Hep distinguished Alpk1 polymorphism, which correlates with mouse susceptibility to bacteria-associated colitis9-12. UDSP-Hep exhibited a stronger Alpk1-mediated antitumour effect and synergized with checkpoint inhibitors. The effect required CD8+ T cells, dendritic cells (DCs) and macrophages, and was sensitive to antibodies that block CXCL10 or CCL2 function. ALPK1 agonists activated DCs for cross-presentation, promoting tumour-specific T cell expansion in the tumour-draining lymph nodes. ALPK1 has wider expression than STING in non-immune cells with a distinct inflammatory signature. UDSP-Hep is differentiated from STING agonists in stimulating tumour-cell antigen presentation, macrophage-DC cross-priming and protective memory T cell differentiation, and it does not induce T cell apoptosis. Our study elucidates the antitumour effect of ALPK1 agonism and suggests the potential of ALPK1 agonists in cancer immunotherapy.