We report on the preparation of tantalum carbide nanopowders via a modified solvothermal synthesis route by using experimental design principles. The reaction proceeds by self-propagating behavior in a molten metal after thermal-ignition of tantalum chloride, carbon, and a metal reductant. A 4 x 4 x 3 experimental design matrix was performed, without replication, to observe the effects of carbon stoichiometry, reductant stoichiometry, and reductant type on process response variables concerning phase purity, compound stoichiometry, crystallite size, particle size, and surface characteristics. Statistical verifications of the observed effects were performed using a 2 x 2 x 2 experimental design matrix with replication. Eleven conditions resulted in phase-pure tantalum carbide, with an additional four nonoxide conditions with low secondary-phase content. The stoichiometry (x in TaC(x)) ranged from 0.92 to 0.96, the average crystallite size ranged from 24 to 68 nm, the specific surface area ranged from 25 to 66 m2/g, and the average particle size ranged from 93 to 123 nm, indicating a low level of agglomeration.