PURPOSE: To provide a treatment method capable of removing the ammonia smell and hydrogen sulfide smell of shellfish fossils consisting essentially of oyster shells and a water quality improving material and filter material produced by this treatment method.

CONSTITUTION: The shellfish fossils are pulverized after drying and the pulverized shellfish fossils are calcined for the necessary time at the temp. which the smell is removed and the effective components do not dissipate. The drying method at this time includes air drying and fan drying which are selected by pulverized grain sizes. The calcination temp. of the pulverized matter is set at about 450°C and the calcination time is most preferably about two hours. The shellfish fossils produced in such a manner are used as the water quality improving material or filter material.