Tantalum nanoparticles have been synthesized by the single-step chemical reaction route. Simultaneous reduction of Tantalum Pentoxide (Ta 2 O 5 ) with the in situ produced hydrogen and carbon at 600°C is a new approach for the production of Ta nanopowder. DH values obtained from thermodynamic calculations are used to predict the entire mechanism of reduction of bulk Ta 2 O 5 into Ta nanoparticles. The results of X-ray diffraction studies show that the final product consists of predominately nano a-Ta with b-Ta as the minority phase. The lattice strain in the final product was calculated using Williamson-Hall formula. The effect of lattice strain on thermal stability of the samples was analyzed by differential scanning calorimetry and thermal gravimetry in the air atmosphere. The morphology and particle size distribution of Ta nanosized powders have been analyzed by scanning electron microscope and transmission electron microscope. The results show that average crystallite size of the product Ta nanopowder is about 2-7 nm.