Ultrafine TaC-5%Co composite powders were synthesized by spray conversion process using tantalum oxalate solution and cobalt nitrate hexahydrate(Co($(NO_3)_2$ . 6$H_2O$). The phase of Ta-Co oxide powders had amorphous structures after calcination below 50$0^{circ}C$ and changed $Ta_2O_5$, $TaO_2$ and $CoTa_2O_6$ phase by heating above $600^{circ}C$. The calcined Ta-Co oxide powders were spherical agglomerates consisted of ultrafine primary particles <50 nm in size. By carbothermal reaction, the TaC phase began to form from 90$0^{circ}C$. The complete formation of TaC could be achieved at 105$0^{circ}C$ for 6 hours. The observed size of TaC-Co composite powders by TEM was smaller than 200 nm.