We fabricated and investigated a 304 stainless steel and carbon nanotube (304SS-CNT) composite with an aim to study its microstructures and high-temperature tensile properties. 304SS powders were mixed with carbon nanotubes using ball milling and consolidated using the spark plasma sintering technique. Tensile specimens made from the consolidated samples of 304SS-CNT were tested in a temperature range from 299 K (26℃) to 773 K (500℃). An induction coil was used for high-temperature tensile tests. The yield strength and the work hardening of the 304SS-CNT sample were found to be higher than those of a sample fabricated from 304SS without carbon nanotubes for all tested temperatures. Microstructure analysis carried out using optical microscopy, scanning electron microscopy, and transmission electron microscopy showed that the 304SS-CNT sample has a microstructure significantly different from the 304SS sample, e.g. reduced grain size and many small cuboidal particles. Composition analysis using energy-dispersive spectroscopy revealed that the cuboidal particles are chromium carbides, and the chromium content is reduced in the 304SS-CNT matrix. Retained carbon nanotubes could not be observed; it is thought that the carbon nanotubes may decompose, induce the reduced grain size and chromium carbides.