The kinetics of calcium release from tablets obtained from modified eggshells in the form of calcium citrate and calcium carbonate was investigated. Calcium release showed the first-order kinetics. After 30 min of the experiment, 79.93% of calcium was released from tablets obtained from modified eggshells in the form of calcium citrate, reaching ~100% after 3 hours. For tablets produced with calcium carbonate, these values were 7 and 60%, respectively. The half-time of calcium release from tablets containing calcium citrate was t_50%= 0.5 h and for tablets containing calcium carbonate it was t_50%= 2.2 h, so calcium in the form of calcium citrate was released 4 times faster. These results can be connected with different solubility of calcium salts. The hardness of tablets with calcium carbonate was by 30 N lower than the hardness of tablets with calcium citrate. It is associated with particular physicochemical properties of calcium salt. Calcium citrate can exist in several states of hydration while calcium carbonate is anhydrous. These properties have an influence on the hardness of tablets.