An extremely high pH, above 10, can occur in sodic soils and even in saline soils after heavy rainfall. The indirect and adverse effects on plant growth that are induced by a high soil pH have been well clarified and include nutritional disorders such as P, Fe and Zn deficiencies and NH3 and HCO3− toxicities. However, studies of the growth injuries induced by the high pH itself are quite limited. We conducted studies to clarify the effect of a high pH on the growth of rice and tomato using a solution culture system developed to eliminate nutrient deficiencies and NH3 and HCO3− toxicities. Although the P, Fe and Zn contents in the shoots were at a sufficiently high level, growth of the tomato and rice was markedly reduced by the high pH conditions (at pH 10 and 11). Our results show the existence of growth injuries in higher plants, induced by a pH above 10. Inhibition of root elongation might be the primary growth disturbance induced by the direct adverse effect of the high pH.