To provide a Nb-silicide based composite achieving both mechanical characteristics and toughness at high levels in an ultrahigh temperature region (1200° C. or more) as well as a high-temperature component and a high-temperature heat engine which employ the same. The Nb-silicide based composite according to the present invention includes 13 to 23 at % of Si, 2.0 to 10 at % of Cr, 5.0 to 23 at % of Ti, 0.0 to 6.0 at % of Al, 0.10 to 8.0 at % of Zr, 1.0 to 8.0 at % of Hf, 0.0 to 2.0 at % of W, 0.10 to 6.0 at % of Sn, 3.1 to 8.0 at % of Mo, 0.20 to 5.0 at % of B, and the balance being Nb and inevitable impurities.