PROBLEM TO BE SOLVED: To provide soil improvement material in which raw material is easily available and a stable neutralizing characteristic is exhibited for a long time, and which does not inhibit the germination and growth of a plant, and to provide a soil improvement method. ! SOLUTION: Improvement material is produced by using natural zeolite as main material and mixing cationic material eluting a cation other than a sodium ion. It is preferable that: the maximum grain size of the natural zeolite is less than 100 μm; cation exchange capacity is 100 meq/100 g or more; the maximum grain size of the cationic material is less than 100 μm; the cationic material is obtained by mixing easily water-soluble material and hardly water-soluble material; and an amount of the cationic material mixed in the natural zeolite is adjusted so that the amount of the cationic material does not exceed the maximum quantity acceptable as a fertilizer component. Water, a fibrous stabilizer, a thickener and a fertilizer comp
