The present study investigated the influence of the content of $Al_2O_3+Y_2O_3$ sintering additives on the microstructure, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites. Phase analysis of composites by XRD revealed mostly of ${alpha}-SiC(4H),;ZrB_2,;{eta}-SiC(15R)$ and In Situ $YAG(Al_5Y_3O_{12})$. The relative density and the flexural strength showed the highest value of 86.8[%] and 203[Mpa] for $SiC-ZrB_2$ composite with an addition of 8[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid at room temperature respectively. Owing to crack deflection and crack bridging of fracture toughness mechanism, the fracture toughness showed 3.7 and $3.6[MPa{cdot}m^{1/2}];for;SiC-ZrB_2$ composites with an addition of 8 and 12[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid at room temperature respectively. Abnormal grain growth takes place during phase transformation from ${eta}-SiC;into;{alpha}-SiC$ was correlated with In Situ YAG phase by reaction between $Al_2O_3;and;Y_2O_3$ additives during sintering. The electrical resistivity showed the lowest value of $6.5{ imes}10^{-3}[({Omega}{cdot}cm]$ for the $SiC-ZrB_2$ composite with an addition of 8[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid at room temperature. The electrical resistivity of the $SiC-ZrB_2$ composites was all positive temperature coefficient(PTCR) in the temperature ranges from $25[^{circ}C];to;700[^{circ}C]$. The resistance temperature coefficient showed the highest value of $3.53{ imes}10^{-3}/[^{circ}C];for;SiC-ZrB_2$ composite with an addition of 8[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid in the temperature ranges from $25[^{circ}C];to;700[^{circ}C]$. In this paper, it is convinced that ${eta}-SiC$ based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.