The effects of impurity (acetic acid, 1.15 mol%) upon the habit changes of NaBrO3 crystals have been investigated. The crystals were grown from aqueous solution under the following conditions: (i) supersaturations: In(C/Ce) = 0-0.24, (Ce: equilibrium mole fraction), (ii) growth temperatures: 20-64 degrees C. The results of habit changes were shown in a plot of growth temperature against supersaturation (such a plot is called a morphodrome). It was found that the impurity effects on the habit changes were more important in the low supersaturation range than in the high supersaturation range.