The protein nanocarrier technology provides various benefits, including the successful delivery of loaded drugs into cancer cells. After delivery, the drug carrier is degraded and expelled from the body. In the present work, corosolic acid-encapsulated kafirin nanoparticles (CA-Kaf NPs) were successfully developed to deliver corosolic acid into MCF-7 cells effectively. Initially, kafirin protein was isolated from sorghum grains and confirmed. Then, corosolic acid was loaded into kafirin protein using a modified desolvation method, and their physicochemical properties, stability, drug release, and cytotoxic potential were investigated. The efficiency of encapsulating corosolic acid into Kaf NPs was 81.13 ± 1.27% and the loading capacity was 8.38 ± 0.51%. The CA-Kaf NPs exhibited an amorphous, spherical shape with a size range of 280–680 nm and a zeta potential of + 2 mV. CA-Kaf NPs released corosolic acid slowly and steadily in an acidic medium (pH 5.4) and are highly biocompatible in a physiological environment. CA-Kaf NPs significantly reduced the viability of MCF-7 cells after 24 h with IC50 value of 58.85 µg × mL− 1 and induced apoptosis. MCF-7 cells treated with CA-Kaf NPs, showed standard apoptotic morphological changes including contracted nuclei and damaged membrane bodies. The release of corosolic acid, from CA-Kaf NPs, leads to a significant increase in reactive oxygen species and damages the mitochondrial membrane potential integrity. These findings imply that CA-Kaf NPs, which target the delivery of corosolic acid into MCF-7 cells and facilitate endocytosis, could have a significant therapeutic potential for breast cancer.