Abstract: The female sterile mutant FS-M₁ was isolated from spontaneous mutation of Brassica napus ‘Ningyou10’. To understand the cellular mechanism of female sterility, we investigated the pollination response and ultrastructure of FS-M₁ papilla cells by fluorescence microscope, scanning electron and transmission electron microscopy. Pollen grains could adhere to and germinate to produce pollen tubes on FS-M₁ papilla cells, but the pollen tubes could not penetrate into papilla cells. FS-M₁ papilla cells became withered and degenerated quickly after flowering. During the degeneration, the number of organelles was significantly decreased; vacuolization was obvious; some organelles such as dictyosome, endoplasmic reticulum, and mitochondria gradually became misshapen and degenerated. Therefore, female sterility in FS-M₁ may have resulted from defects in papilla cells.