Acid precipitation is presently a major environmental issue worldwide and a great deal of information concerning the effects of acid precipitation on terrestrial ecosystems is becoming available. This review describes the status of acid precipitation in Japan and the impact of acid precipitation on the growth of agricultural crops and forest trees. Annual mean pH value of precipitation in Japan which was about 4.7 did not change significantly in the past decade. The acidity of rainwater which was caused by H₂SO₄ and HNO₃ mainly was neutralized by alkaline species such as NH₃ and Ca²⁺ in urban areas. In simulated acid rain experiments, visible foliar injury of most of the crop species and some sensitive tree species occurred at pH values below 3.5 and pH 3.0, respectively. It has been suggested that the decrease in intercellular pH levels is one of the possible mechanisms of occurrence of foliar injury. Acid rain droplets on leaves accelerate the leaching of cellular materials such as minerals, amino acids, proteins and carbohydrates, which may neutralize acidic rain droplets on the leaf surfaces. Since these materials which contribute to the buffering system of plants were leached by acid rain, residual H⁺ ions may penetrate into the leaf tissues across the cuticular layer, and lead to the increase of the acidity in leaf tissues and development of foliar injury symptoms.