Rice plant body is consisted of some ma t u red leaf sheaths and some growing young leaves, and the shoot apex exists in the most inner part of the plant body, i.e. the shoot apex is surrounded by those growing young leaves and matured leaf sheaths. In the plant body two kinds of air space, the interfoliar air space and the intercellular air space or lysigenic air space, exist. The former exists between matured leaf sheaths and growing young leaves, and the latter exists in matured leaf sheaths and in growing young leaves. The author thought that these air spaces might have some effects on the growth of young leaves. In this study, the volume and percentage against the cross section of these air spaces were examined. The following results were obtained. 1. Rice seedlings of 6.0, 6.3, 6.5, 6.7 and 7.0 leaf stages were used to investigate the change of air spaces from the beginning to the end of 1 plastochrone. The change of the volume of air spaces within 1 plastochrone was great at the upper portion of the plant body and no significant change was observed at the basal portion. Each percentage of interfoliar and intercellular air spaces against the cross section was little at the beginning of plastochrone and increased with the proceeding of plastochrone. 2. Rice seedlings of 3, 6 and 9 leaf stages were used to examine the change of air spaces with the seedling growth. The volume of interfoliar air space in the plant body did not change with the growth of rice plant. On the other hand, the volume of intercellular air space somewhat increased with the growth of rice plant. The change of percentage of the air spaces against the cross section with the growth of plant was the same as the volume of the air spaces. 3. The volume of interfoliar and intercellular air spaces and the percentage of the air spaces against the cross section did not vary in three varieties (Norin No. 15; early maturing variety, Hoyoku and Norin No.18; late maturing varieties). 4. The volume of interfoliar air space surrounding the shoot apex directly was almost the same in all cases.