Oryza meyeriana Baill (GG genome) is a precious germplasm in the tertiary gene pool of cultivated rice (AA genome),and possesses important traits such as resistance and tolerance to biotic and abiotic stress. However, interspecificcrossability barrier, a critical bottleneck restricting genes transfer from O. meyeriana to cultivars has led to no hybridsthrough conventional reproduction. Therefore, the reasons underlying incrossability were investigated in the present report.The results showed that: (i) at 3–7 d after pollination (DAP), many hybrid embryos degenerated at the earlier globular-shapedstage, and could not develop into the later pear-shaped stage. Meanwhile, free endosperm nuclei started to degenerate at1 DAP, and cellular endosperm could not form at 3 DAP, leading to nutrition starvation for young embryo development;(ii) at 11–13 DAP, almost all hybrid ovaries aborted. Even though 72.22% of hybrid young embryos were produced in theinterspecific hybridization between O. sativa and O. meyeriana, young embryos were not able to further develop into hybridplantlets via culturing in vitro. The main reason for the incrossability was hybrid embryo inviability, presenting as embryodevelopment stagnation and degeneration since 3 DAP. Some possible approaches to overcome the crossability barriersin the interspecific hybridization between O. sativa and O. meyeriana are discussed. Oryza meyeriana Baill (GG genome) is a precious germplasm in the tertiary gene pool of cultivated rice (AA genome), and possesses important traits such as resistance and tolerance to biotic and abiotic stress. However, interspecificcrossability barrier, a critical bottleneck restricting genes transfer from O. meyeriana to cultivars has led to no hybrid sthrough conventional reproduction. reproduction, the reasons underlying underlying incrossability were investigated in the present report that results showed that: (i) at 3-7 d after pollination (DAP), many hybrid embryos degenerated at the earlier globular-shaped stage, and could not develop into the later pear-shaped stage. And, free endosperm nuclei started to degenerate at 1 DAP, and cellular endosperm could not form at 3 DAP, leading to nutrition starvation for young embryo development; ( ii) at 11-13 DAP, almost all hybrid ovaries aborted. Even though 72.22% of hybrid young embryos were produced in theinterspecific hybridization between O. s ativa and O. meyeriana, young embryos were not able to further develop into hybrid plantlets via culturing in vitro. The main reason for the incrossability was hybrid embryo inviability, presenting as embryodevelopment stagnation and degeneration since 3 DAP. Some possible approaches to overcome the crossability barriersin the interspecific hybridization between O. sativa and O. meyeriana are discussed.