I 4 ¯ -carbon was first proposed by Zhang et al., this paper will report regarding this phase of carbon. The present paper reports the structural and elastic properties of the three-dimensional carbon allotrope I 4 ¯ -carbon using first-principles density functional theory. The related enthalpy, elastic constants, and phonon spectra confirm that the newly-predicted I 4 ¯ -carbon is thermodynamically, mechanically, and dynamically stable. The calculated mechanical properties indicate that I 4 ¯ -carbon has a larger bulk modulus (393 GPa), shear modulus (421 GPa), Young's modulus (931 GPa), and hardness (55.5 GPa), all of which are all slightly larger than those of c-BN. The present results indicate that I 4 ¯ -carbon is a superhard material and an indirect-band-gap semiconductor. Moreover, I 4 ¯ -carbon shows a smaller elastic anisotropy in its linear bulk modulus, shear anisotropic factors, universal anisotropic index, and Young's modulus.