To provide a dental glass ionomer cement for a sealer to be used for sealing a gap between a gutta-percha point filled in a root canal in a dental root canal treatment and a root canal wall, with a prolonged setting time and with sufficient setting property even in a root canal having much water content, the dental cement for a sealer includes a polymer of .alpha.-.beta. unsaturated carboxylic acid, oxide powder capable of reacting with the polymer of .alpha.-.beta. unsaturated carboxylic acid, and water, and further includes an organic acid salt of metal selected from Mg, Ca, and Sr and/or a hydroxide of metal selected from Mg, Ca, and Sr.