Hydrogen storage alloys can absorb and desorb a large amount of hydrogen per unit volume at room temperature and pressure. Hydrogen storage alloys have considerable potential so that they are expected to apply to hydrogen storage tanks, chemical compressors and chemical heat pumps. However, volume expansion ratio of LaNi5 alloy is approximately 24 % with hydrogen absorption. Stress of wall of hydrogen storage tank increase with an increase in an alloy packing fraction, hence tank deformation and breakage may occur. In this study, heat transfer and stresses in tanks and packed beds of hydrogen storage alloys with expansion are numerically analyzed with finite element method to investigate the effect of dimension (height and radius) on stresses with hydrogen absorbing fraction in the cylindrical packed beds and tanks. First, temperature and hydrogen absorbing fraction in the packed beds are calculated respectively. Then hydrogen absorbing fraction distributions are used to calculate the stress in the tank and the packed bed, assuming alloy’s volume expansion ratio is linear to hydrogen absorbing fraction and is isotropic for each axis. As a result, it is shown that hydrogen absorbing proceeds from the wall side, where the heat can be removed efficiently by coolants. The maximum wall stress of all tanks increases with an increase in hydrogen absorbing fraction in the packed beds. The dimension of all the packed beds and all the hydrogen absorbing fractions has a significant influence on the maximum wall stress.