In order to investigate the biological effects of conformational changes in the folding state of bovine α-lactalbumin (α-La), the protein was prepared and classified as apo form, microbial transglutaminase (MTGase) added form, or bovine α-La made lethal to tumor cell (BAMLET) form. Apo α-La form showed weaker cancer cell inhibitory activity (apoptosis) than native α-La, which suggests that the metal ion-like Ca2+ had a positive effect, whereas BAMLET form showed strong cancer cell apoptotic activity. The BAMLET form seemed to be a molten globule structure that increased hydrophobicity. MTGase added to apo α-La polymer showed similar anti-cancer activity as native α-La, and it was well hydrolyzed by digestive enzymes. NMR results showed that BAMLET interacted with oleic acid and produced a complex.