The effect of $Al_2O_3$ additives to $eta-SiC+39vol.%ZrB_2$ electroconductive ceramic composites by pressureless sintering on microstructural, mechanical and electrical properties were investigated. The $eta-SiC+39vol.%ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_2O_3$ powder as a liquid forming additives at $1950^{cire}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $alpha-SiC(6H), ZrB_2$ and weakly $alpha-SiC(4H), eta-SiC (15R)$ phase. The relative density of composites was lowered by gaseous products of the result of reaction between eta-SiC and Al_2O_3$, therefore, porosity was increased with increasing $Al_2O_3$ contents, and showed the maximum value of 1.4197MPa.$m^{1/2}$ for composite with 4wt.% $Al_2O_3$ additives. The electrical resistivity of $eta-SiC+39vol.%ZrB_2$ electroconductive ceramic composite was increased with increasing $Al_2O_3$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature range of $25^{cire}C$ to $700^{cire}C$.