Chalcone synthase (CHS) is a key enzyme in the biosynthesis of all classes of flavonoids in plants. An antisense or sense CHS cDNA of tea under the regulation of a tapetum-specific promoter of rice was introduced into tobacco by Agrobacterium-mediated. transformation. A reduction in the number of fertile pollen grains was observed in four out of 27 antisense CHS transformants and in five out of 26 sense CHS transformants. The distorted pollen grains of transformants lacked starch and flavonols. Fluorescein diacetate staining indicated abortion started at the late uninucleate microspore stage. The antisense or sense transgene would affect the pollen fertility.