An 1.4 kb of the fad3 cDNA encoding microsomal linoleic acid desaturase catalyzing the conversion of linoleic acid (18:2, ω-6) to linolenic acid (18:2, ω-3) was introduced into tobacco plants by the Agrobacterium-mediated plant transformation. Among the transgenic tobacco plants conferring kanamycin resistance, five transformants showing increment in unsaturated fatty acid contents were selected and further analyzed for the transgenecity. In genomic Southern blot analyses, copy numbers of the integrated fad3 DNA in chromosomal DNA of the five transgenic tobacco plants were varied among the transgenic lines. By Northern blot analyses, the abundancy of the fad3 mRNA transcript directed by Cauliflower Mosaic Virus 35S promoter was consistent with the relative copy number of the fad3 DNA integrated in the chromosome of transgenic tobacco plants. When compared with the wild type, accumulation of linolenic acid in transgenic tobacco roots was elevated 3.7- to 4.7-fold showing a corresponding decrease in the linoleic acid contents; however, slight increments for linolenic acid were noticed in transgenic leaf tissues. These results indicated that the elevated level of fad3 expression is achieved in transgenic tobacco plants.