Crown structure dynamics of Kandelia obovata (S., L.) Yong stands were investigated over four years. Tree height H, height at the lowest living leaves H_L and stem diameter at H/10 D_0.1H were measured. Tree crown parameters, such as crown length C_L and crown width C_W, were also measured. Height at the lowest living leaves H_L increased significantly, so that crown length C_L decreased as stands grew. It suggests that crown changes to be dumpy as stands grow. Crown width C_W increased and then decreased as stands grew, which means that crown width attains its maximum size and then decreases just after the canopy closes. The C_L/C_W ratio decreased as stands grew, which indicates that the crown shape changes from a thick type to a thin type with stands grow. It may imply that trees transform their crown shape for reducing the stress of competition. The year when crown width C_W becomes maximum decreased from the riverside landward, which indicates that trees near the riverside later attain the year as compared with trees near the landward.