To investigate the effect of carbon on the sintering behavior of ladle filler sands, laboratory experiments are carried out using chromite‐based filler sands and carbon (graphite) powders as well as liquid steel in an inert atmosphere at 1600 °C. It is found that the fine carbon powders result in an increase in angle of repose before sintering. After sintering, the apparent porosity increases with the carbon content in the sands, while the bulk density declines. During sintering with and without liquid steel, the carbon powders in the sands will react with the sand grains, leading to the generation of some gases (CO and CO2) and the increase of liquid phase in the sands. The acceleration of the formation of the liquid phase in the sands would enhance the sintering of the sands. The generated gases can result in many large holes in the sands, and liquid steel is very possible to infiltrate into the sands. To obtain a higher ladle free opening rate, special attention should be paid to carbon addition in ladle filler sands.