In order to make clear the reason why there are differences in the grain shedding among varieties of Japonica-Indica hybrid rice, morphology of the abscission region in longitudinal sections of the pedicel was investigated. Also, the strength required to detach rice grain from its pedicel was measured with an unbonded strain gauge transducer and a null balancing recorder. All the examinations were made at harvest time. Experimental materials used were 27 varieties of Japonica-Indica hybrid rice bred in Korea and 7 varieties of their parents. The results obtained are as follows: 1. Degree of grain shedding of Japonica-Indica hybrid rices was similar to that of Indica type parents and weaker than that of Japonica type parents (Table 2). 2. In all the Japonica-Indica hybrid varieties, parenchymatous cells presented in the abscission layer have completely collapsed at the harvest time. Regarding their parents, the parenchymatous cells have collapsed in the Indica type parents such as Peta, IR 8, IR 24, and Taichung native 1, while no abscission layer was observed in the two Japonica type parents, Yukara and Jinheung, and one Indica type parent, Dee-Geo-Woo-Gen. 3. Among the Japonica-Indica hybrid varieties, highly positive correlation was observed between degree of grain shedding and thickness of the supporting zone consisting of the central vascular tissues and the sclerenchymatous cells (Fig. 1, 2 and 3). Since the thickness of the central vascular tissues was almost same among the varieties (mean value: 88±6.6μm), it may be concluded that varieties with the thinner sclerenchymatous tissue situated between the abscission layer and the central vascular bundle are essentially more fragile.