In this study, calcium lanthanum sulfide (CaLa2S4, CLS) ceramics with the cubic thorium phosphate structure were sintered at different temperatures by field-assisted sintering technique (FAST). Densification behavior and grain growth kinetics were studied through densification curves and microstructural characterizations. It was determined that the densification in the 850 degrees C-950 degrees C temperature range was controlled by a mixture of lattice or grain-boundary diffusion, and grain-boundary sliding. It was revealed that grain-boundary diffusion was the main mechanism controlling the grain growth between 950 degrees C and 1100 degrees C. The infrared (IR) transmittance of the FAST-sintered CLS ceramics was measured and observed to reach a maximum of 48.1% at 9.2 mu m in ceramic sintered at 1000 degrees C. In addition, it was observed that the hardness of the CLS ceramics first increased with increasing temperature due to densification, and then decreased due to a decrease in dislocations associated with grain growth.