In order to examine the mechanical properties of a biomedical Co-33Cr-5Mo-0.3N alloy at elevated temperatures, tensile tests have been conducted in the temperature range from room temperature to 1373 K at initial strain rates of 1.0×10⁻¹ s⁻¹ and 1.4×10⁻⁴ s⁻¹. The 0.2% proof stress and the tensile strength as a function of temperature have the plateau and the hump, respectively, at intermediate temperatures. The elongation to fracture increases at intermediate temperatures and abruptly decreases at higher temperatures. The decrease of the elongation at higher temperatures arises from the intergranular fracture, possibly caused by the equilibrium segregation of harmful elements such as sulfur. The serrations on the stress-strain curves are observed at intermediate temperatures. The temperature range where the elongation is enhanced and the serrations appear is shifted to lower temperatures at a low strain rate. The 0.2% proof stress does not increase with increasing strain rate and the strain rate sensitivity exhibits negative values at intermediate temperatures. It is considered that a serration leading to large elongation results from the dynamic strain aging.