The effect of strain rate and environment on the mechanical behavior at different temperatures of the Ni-19Si-3Nb-0.15B-0.1C alloy is investigated by atmosphere-controlled tensile testing under various conditions at different strain rates and different temperatures). The results reveal that the Ni-19Si-3Nb-0.15B-0.1C alloy exhibits ductile mechanical behavior (UTS ∼ 1250 MPa, ε ∼ 14%) at temperatures below 873 K under different atmosphere conditions. However, the alloy without boron and carbon addition shows ductile mechanical behavior only when the sample is tested in vacuum. This indicates that the microalloying of boron and carbon does overcome the environmental embrittlement from water vapor at test temperatures below 873 K for the Ni-19Si-3Nb base alloy. However, the boron and carbon doped alloy still suffers from embrittlement associated with oxygen at a medium high temperature (i.e. 973 K). In parallel, both of the ultimate tensile strength and elongation exhibit quite insensitive response with respect to the loading strain rate when tests are held at temperatures below 873 K. However, the ultimate tensile strength exhibits high dependence on the strain rate in air at temperatures above 873 K, decreasing the ultimate tensile strength with decreasing strain rate.