Despite notable advancements, the significantly improved yet suboptimal heating efficiency of current magnetic nanoparticles hinders the effectiveness of systemically delivered magnetic hyperthermia in reducing tumor size or halting growth. Addressing this challenge, the seed-and-growth thermal decomposition method has been developed to synthesize cobalt-doped iron oxide nanoparticles featuring a cubical bipyramid morphology and consisting of both magnetite and maghemite phases within their nanostructure. They possess an exceptional specific absorption rate of 14,686 ± 396 W g Fe, inducing a temperature rise of 3.73°C per second when subjected to an alternating magnetic field (315 kHz; 26.8 kA m). The cubical bipyramid-shaped nanoparticles, functionalized with a cancer-targeting LHRH peptide, efficiently accumulate in ovarian cancer xenografts following an intravenous injection at a relatively low dose of 4 mg kg, elevating intratumoral temperatures beyond 50°C with a highly efficient heating rate. In contrast to previously reported magnetic nanoparticles with ultrahigh heating efficiency, the developed cubical bipyramid-shaped nanoparticles effectively halt ovarian cancer tumor growth after a single 30-minute session of magnetic hyperthermia. These outcomes underscore the profound potential of shape-dependent magnetic hyperthermia, where the unique cubical bipyramid morphology significantly enhances the heating efficiency and therapeutic efficacy of magnetic nanoparticles, revolutionizing the design of magnetic nanomaterials and significantly improving the effectiveness of hyperthermia-based cancer treatments.