Recent findings have positioned the gut microbiota as a promising target to enhance cancer immunotherapy. However, the specific microbial molecules that drive anti-tumor immunity remain unclear. Here, we identify a human-derived strain, Lactobacillus fermentum MI37, that potentiates anti-cancer immune responses and synergizes with anti-PD-1 immune checkpoint blockade. MI37 robustly induces IFN-γ production by splenocytes, with minimal IL-10 induction, and enhances cytotoxic T lymphocyte infiltration and inflammatory gene expression within tumors in a syngeneic mouse model. Remarkably, heat-killed MI37 retains its immunostimulatory effects and anti-tumor efficacy. Fractionation experiments implicate lipoteichoic acid (LTA) as the active component, and LTA mimics the effects of MI37 on IFN-γ production and CD8⁺ T cell activation. Genomic and proteomic profiling reveals MI37-specific pathways involved in teichoic acid biosynthesis, including a unique sulfatase N-terminal domain-containing protein with an LTA synthase domain. These findings highlight the potential of LTA-producing probiotics as microbial adjuvants to improve the efficacy of cancer immunotherapy.