Crown shape dynamics of Kandelia obovata Shue, Liu & Yong stands were investigated over five years. Tree height H (m), height at the lowest living leaves H_L (m), crown length C_L (m) and crown width C_W (m), were measured. The H_L increased with increasing H, but the increasing rate of H_L was much higher than that of H. As a result, C_L changed to be dumpy as the stands grew. On the other hand, C_W attained its maximum and then decreased, though C_W of a young stand still increased. The inequality of C_L became small as the stands grew, while that of C_W was almost constant. The crown shape changed from a thick type to a thin type as the stands grew. These results may imply that trees transform their crown shape for reducing the stress of competition. The age of trees when C_L and C_W attain their maximum decreased and then increased from the riverside landward, which means that trees near the riverside and the landward later attain their maximum C_L and C_W than trees in the middle area. The present results suggest that the crowded mangrove stands have their own mechanisms to function with developing stands.