Combination therapy via nanoparticulate systems has already been proposed as a synergistic approach for cancer treatment. Herein, undecylenic acid modified thermally hydrocarbonized porous silicon nanoparticles (UnTHCPSi NPs) loaded with sorafenib and surface-biofunctionalized with anti-CD326 antibody (Ab) were developed for cancer chemo-immunotherapy in MCF-7 and MDA-MB-231 breast cancer cells. The cytocompatibility study showed no significant toxicity for the bare and antibody-conjugated UnTHCPSi (Un-Ab) NPs at concentrations lower than 200 μg·mL^-1. Compared to the bare UnTHCPSi, Un-Ab NPs loaded with sorafenib reduced the premature drug release in plasma, increasing the probability of proper drug targeting. In addition, high cellular interaction and subsequent internalization of the Un-Ab NPs into the cells expressing CD326 antigen demonstrated the possibility of improving antigen-mediated endocytosis via CD326 targeting. While an in vitro antitumor study revealed a higher inhibitory effect of the sorafenib-loaded Un-Ab NPs compared to the drug-loaded UnTHCPSi NPs in the CD326 positive MCF-7 cells, there was no difference in the anti-proliferation impact of both the abovementioned NPs in the CD326 negative MDA-MB-231 cells, suggesting CD326 as an appropriate receptor for Ab-mediated drug delivery. It was also shown that the anti-CD326 Ab can act as an immunotherapeutic agent by inducing antibody dependent cellular cytotoxicity and enhancing the interaction of effector immune and cancer cells for subsequent phagocytosis and cytokine secretion. Hence, the developed nanovectors can be applied for simultaneous tumor-selective drug targeting and immunotherapy.