The present invention provides a cellulose ester in which heat resistance under wet condition is compatible with both releasability and spinnability even when the amount of the residual solvent is small in a casting process. The cellulose ester fulfills the following formula: 0.5<(B)/(A)<1.5 wherein (A) and (B) represent the total amount (in terms of molar amount) of residual sulfuric acid in 1 gram of the cellulose ester and the total amount (in terms of molar amount) of calcium contained in 1 gram of the cellulose ester, respectively.