Insect larvae have become a prominent source of bioactive proteins and peptides. The antimicrobial, antioxidant, and cytotoxic activities of proteins and peptides from Hermetia illucens L. larvae (BSFL) have been studied. However, the correlation between antioxidant and cytotoxic activities, as well as the effect of protein and peptide size on cancer cells, specifically MCF-7 breast cancer cells, remains underexplored. This study aims to evaluate the total antioxidant capacity (TAC) and cytotoxic activity of BSFL proteins and peptides against MCF-7 cells. Proteins and peptides were extracted through alkaline extraction and acid precipitation, followed by ultrafiltration with 3 kDa and 30 kDa MWCO to obtain crude protein, protein >30 kDa, and protein-peptide 3-30 kDa. The 3-30 kDa sample exhibited the highest TAC (379.054 μmol/mg protein), while the >30 kDa sample had the lowest (241.918 μmol/mg protein). After a 48-hour incubation, crude protein and protein >30 kDa showed cytotoxicity against MCF-7 cells with IC₅₀ values of 83.44 μg/mL and 82.98 μg/mL, respectively, while the 3-30 kDa protein-peptide showed no cytotoxic effects. These results indicate that cytotoxic activity is inversely related to antioxidant capacity. In conclusion, crude protein and >30 kDa protein from BSFL exhibit potential anticancer properties, while 3-30 kDa protein-peptides have high antioxidant capacity without affecting cancer cells.