Great efforts have been made to manipulate nanoparticles (NPs) with a diameter of 10–100 nm to passively target lymph nodes (LNs) to magnitude anti-tumor activity of T cells. However, no attention has been paid to increasing the retention of NPs with active affinity in order to induce a prolonged release of antigens or molecular adjuvants in the LNs mattering the immune response. Here, we formulated two NPs encapsulated with imiquimod (IMQ), a TLR7/8 agonist, and paclitaxel (PTX) and further modified them with tannic acid (TA), respectively, to generate IMQ NP and PTX NP with a final diameter of approximately 40 nm. Attributing a strong affinity of TA molecules to the elastin of LN conduits, the TA modified IMQ NPs can bypass the gaps in the layer of lymphatic endothelial cells and enter the paracortex through the lymph node capsule-associated (LNC) conduits. Similarly, the TA modified PTX NPs increased delivery of PTX to the metastatic tumor site in LNs, where the tumor-associated antigens were released and presented by conduits-lining dendritic cells to activate T cells. Thus, the NPs with deposition to LN conduits showed excellent performance in preventing lymphovascular invasion of triple-negative breast cancer cells and lung metastasis thereafter. On the contrary, the NPs without TA flowed through the subcutaneous sinus existing LNs directly by efferent lymphatic vessels showing relatively poor therapeutic outcomes. This study reveals that TA may mediate the long retention of antigens and molecular adjuvants to be delivered to deep LNs for developing potent vaccination technology.