This study was conducted to enhance stem firmness on standard chrysanthemum 'Baekma' bred in Korea for commercial quality and inhibition of stem breaking during transportation through foliar spraying with calcium agent. Calcium agent screening for 'Baekma' was examined using CaCl₂·2H₂O, Ca(NO₃)₂·4H₂O, and OS-Ca (natural liquid calcium agent extracted from oyster shell) depending on each concentration (0, 0.001, 0.01, 0.1, and 1.0%, respectively). All calcium agents which were sprayed with 1.0% showed chemical injury such as stem bending or leaf burn. OS-Ca also showed the most sensitive response to chemical injury than other calcium agents because OS-Ca was very absorbent to 'Baekma'. Maximum stem firmness measured at final harvesting stage was the hardiest in OS-Ca than in other calcium agents. Especially, maximum stem firmness was the strongest in 0.01% OS-Ca. However, elastic strength and maximum bending stress was the strongest in 0.001% OS-Ca than in the others. Thus, OS-Ca ranged from 0.005 to 0.05%, which did not show any chemical injury, was finally selected as 1st candidate for hardening stem firmness of 'Baekma'. The next experiment using OS-Ca was conducted with the concentrations of 0, 0.005, 0.01, and 0.05%, respectively. From the results, 0.05% OS-Ca showed the best plant growth in almost parameters such as plant height, stem diameter (upper and middle part), the number of leaves, and dry weights of each part than the other concentrations of OS-Ca and control. As for stem firmness depending on OS-Ca concentration, moreover, the Ca content within stem, maximum firmness, elastic strength, and maximum bending stress of stem in 'Baekma' sprayed with 0.05% OS-Ca showed the highest values among all treatments and it turned out to be very high level of significance between control and OS-Ca treatments. However, the area and percentage of inside cavity within horizontal stem section in 'Baekma' did not showed any significance between all treatments including control. Thus, stem firmness of 'Baekma' did not show any correlation with the inside cavity area of stem. In conclusion, it was recommended to enhance stem firmness of 'Baekma' during transportation, 0.05% OS-Ca might be the most proper concentration for foliar-spraying at vegetative growth stage of 'Baekma'.