Sintering behavior of tungsten (W) and tantalum (Ta) powders were investigated by field assisted sintering technology (FAST). The results show that tungsten powder (0.6-0.9 μm) was sintered to around 99% relative density at 2000°C under 85 MPa pressure for 30 minutes. The same density was achieved in tantalum powder (5.3 μm) sintered at 1850oC under 55-75 MPa pressure for 5 minutes. However, the corresponding grain sizes were 22.2 μm for tungsten, and above 50 μm for tantalum. With 10 vol% nano WC additive, 99% relative density was achieved at lower sintering temperature in both materials (1700°C for W and 1750°C for Ta). Furthermore, sintered grain size was reduced to 2.9 μm for W and less than 10 μm for Ta, when WC additive was used. X-ray diffraction results revealed that some W reacted with WC and formed W2C phase, which remained after sintering. Ta 2C phase was detected in the Ta samples with WC additive.