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Abstract: A comparative analysis of electronic structure and stability of endohedral metallofullerenes TM@C24 and TM@C24H12 (TM=Ti, Zr and Hf) is systematically performed with the aid of quantum chemical DFT-B3PW91 approach. Our calculated results show that TM@C24H12 display higher symmetry compared with TM@C24, and all of endohedral metallofullerenes are in a singlet spin state. Thermodynamic data reflect that endohedral metallofullerenes TM@C24 are more stable than TM@C24H12 and the Ti atom is energetically favorable to be encapsulated. However, these TM@C24H12 have higher kinetic stability. The analyses of the vertical electron affinities (VEAs) and vertical ionization potentials (VIPs) indicate the possibilities of accepting electrons of TM@C24H12 become weaker and the possibilities of denoting electrons become stronger. Additionally, natural population analysis presents that the natural charge on TM atoms dramatically increases along with increasing atomic number, and the 5d orbitals of Zr atom and 6d orbitals of Hf atom are significantly involved in their chemical bonding. [Copyright &y& Elsevier]