A new carbon dioxide sequestration process was proposed. The process consists mainly of a calcium extraction step from concrete sludge by water dilution with stirring and a calcium carbonate precipitation step by the reaction of extraction solution and gaseous carbon dioxide. Experimental data for the proposed process was obtained using real concrete sludge generated from a concrete pole/pile plant. The influences of water dilution ratio (weight ratio: 3-50) and extraction treatment time (5-40 min) on the calcium extraction rate from concrete sludge were investigated. It was confirmed that the calcium concentration in water increased sufficiently for calcium carbonate to be precipitated by the reaction with gas containing carbon dioxide (10%). In the range of experimental conditions studied, the dilution ratio of 20 and the extraction time of 5 min were found to be the optimal treatment conditions for calcium extraction from concrete sludge. The calcium carbonate precipitation step from calcium solution is easily accelerated by the addition of seed crystals. These results indicate that concrete sludge can be used as a cheap calcium resource for carbon dioxide sequestration.