The development of epsilon-negative materials is essential for many applications in smart electronics and modern information technology because of their enticing properties. Numerous efforts have been done in terms of diluted metal. However, no more attempt has been made from increasing electron density. And the effect of doping on negative permittivity is still unclear. In this work, mono-phase LaCo1-xNixO3 ( =0.06, 0.1, 0.12, 0.16, 0.2) was prepared through a sol-gel technique and subsequent sintering. Electronic structure, electrical properties, and negative permittivity properties are investigated in detail, and the correlation between electrical conductivity and negative permittivity is elaborated in terms of electrodynamics.