Microsomal Ω-3 fatty acid desaturase (FAD3) is an essential enzyme in the production of the n-3 polyunsaturated fatty acid α-linolenic acid during the seed developing stage. To understand the regulatory mechanism of the gene encoding the Ω-3 fatty acid desaturase, a genomic fragment corresponding to the previously isolated perilla seed PfFAD3 cDNA was amplified from perilla (Perilla frutescens Britt) by GenomeWalker PCR. Sequence analysis of the fragment provided with identification of a 1485-bp 5'-upstream region and a 241-bp intron in the open reading frame. To determine the tissue-specificity of the PfFAD3 gene expression, the 5'-upstream region was fused to the β-glucuronidase (GUS) gene and incorporated into Arabidopsis thaliana. Histochemical assay of the transgenic plants showed that GUS expression was restricted to seed and pollen, showing that PfFAD3 gene was exclusively expressed in those tissues.