Abstract: The activated kaolin powder compound is prepared from naturally-existing kaolin (hereinafter "natural kaolin"). The activated kaolin powder compound is prepared by heating natural kaolin to 480.degree. C. within at most one hour, calcinating the heated kaolin at high temperature by heating to 980.degree. C. over at least one hour, quenching the calcinated kaolin with water or air, and pulverizing the quenched kaolin to give particle sizes of 2 .mu.m or less. The activated kaolin powder compound is employed in an amount of about 5 to 15% by weight of cement for preparing mortar or cement. The cement composition containing the activated kaolin powder compound can provide a mortar or concrete having superior properties in compressive strength, flexural strength and water permeability.