The experiment was made to determine the invisible injury to rice plants by photochemical oxidants. Rice plants were grown in two filon chambers, the one with filtered ambient air and the other with unfiltered a ambient air, for the experimental period from transplanting to harvesting at the Central Agricultural Experiment Station, Konosu, Saitama. The rice plants in the filtered ambient air chamber were compared with those in the unfiltered ambient air chaember on growth, yield and visible injury of photochemical oxidants. Both the visible injuries on leaf blade and invisible injuries such as the reduction of the growth and rate of photosynthesis were observed in the unfiltered ambient air chamber. On the otherhand, no injuries were detected in the filtered air chamber. The rice plants in the filtered ambient air chamber were more numerous in number of panicles and spikelets per hill and in percentage of ripened grains, and higher in yield than those in the unfiltered one. It may be suggested that the reduction in growth and yield of rice plants in the unfiltered chamber could be mainly due to photochemical oxidants, because of high concentration of photochemical oxidants, averaged 3.74 pphm hourly monitored in Konosu, during the experimental period from 6th of June to 15th of October.