Abstractipening is a complex developmental process involving changes in the biochemistry,physiology and geneexpression of the fruit．Tomato polygalacturonase(PG;E．C．3．2．1．15)is expressed only during the ripen - ing stage of fruit development and has a major role in cell wall degradation．To demonstrate the function ofPG in the fruit ripening,a chimaeric gene containing the cauliflower mosaic virus 35S promoter and a full - length PG 1．9kb cDNA in reverse orientation was constructed．The construct was integrated into thetomato genome by Agrobacterium - mediated transformation．Examination by PCR showed that the chi - maeric antisense PG gene was stably integrated into the transgenic tomato chromosome．Furthermore,analysis of transcription in the mature transgenic tomato fruits indicated the expression of the antisense PGgene and a remarkable reduction in PG mRNA．These results demonstrated the ability of antisense PGgene to inhibit fruit endogenous PG gene expression in the whole tomato plants．The function of PG in thefruit softening was discussed．The approach which we have used to study fruit ripening will have generalapplicability in agricultural production．