The influence of carbon additions on the proper ties of a complex niobium alloy, Nb-10W-5V-1Zr (B-77), was investigated. Carbon additions of 0.077 and 0.15 w/o refined the as-cast grain size and increased hardness. For the conditions of heat treatment investigated, the carbon level had no effect on the 1205 C (2200 F) stress rupture strength of B-77, but the carbon containing al loys had higher rupture strains than low carbon B-77. Heat treatment studies did not show any evidence of precipitation hardening effects, however solution annealed and cold rolled B-77 0.15 C material gave significantly higher hot hardness values than solution annealed materials, suggesting that carbide precipitation on disloca tions was contributing to high temperature strength. Preliminary data showed grain boundary sliding occurred in B-77 during creep testing at 1205 C (2200 F).