The intravesical instillation of live Bacillus Calmette-Guerin (BCG) for treating bladder cancer is a powerful cancer immunotherapy. The BCG cell wall skeleton (BCG-CWS) is the main component of the adjuvant, leading to the induction of antitumor immunity. However, the use of live BCG and BCG-CWS is currently limited to local administration because of the infectiousness of live BCG and the insolubility of BCG-CWS. We previously developed a water-dispersible nanoparticle (NP) formulation of BCG-CWS (CWS-NP), which could be used to apply BCG components for use as a systemically injected adjuvant for the treatment of cancers other than bladder cancer. In the present study, we examined the possible use of CWS-NP for cancer immunotherapy, when intravenously administered. The CWS-NP was a highly uniform dispersion and showed no aggregation in serum. The intravenously injected CWS-NP accumulated in the spleen and was efficiently taken up by dendritic cells, leading to their maturation. The coadministration of CWS-NP and ovalbumin (OVA) loaded NP resulted in the generation of OVA-specific cytotoxic T cells and inhibited the growth of E.G7-OVA tumors. These results represent the first findings related to the use of systemically injected CWS-NP as an adjuvant for cancer immunotherapy.