PURPOSE: To provide a process for producing a Ca-type zeolite usable as a preferable soil improver by using waste coal ash as a starting substance.

CONSTITUTION: A mixture of coal ash and an aqueous solution of alkali is optionally incorporated with a silicic acid enriching material or an aluminum enriching material and the obtained mixture is subjected to thermal reaction to produce a zeolite. In the above process, the reaction product is dehydrated and incorporated with limestone powder and water and the obtained slurry is neutralized under stirring while keeping its pH to >4 and, at the same time, Na ion is replaced with Ca ion.