The first intron (EPI) of rice 5-enolpyruvylshikimate 3-phosphate synthase gene was isolated by PCR from one clone with genomic EPSP synthase gene. Sequence analysis showed that the first intron is 704 bp in length with 36.2% G+C content. To investigate its effect on expres-sion of foreign gene, we inserted the first intron between CaMV35S promoter and b-glucuronidase (GUS) gene. The transient expression results showed that GUS could be expressed effectively with EPI. The GUS activity in transgenic tobacco shows that the EPI can greatly enhance the ex-pression level of b-glucuronidase (P < 0.01) compared with transgenic tobacco without the first intron, and 3- to 6-fold increase in GUS activity in some transgenic tobaccos. Northern blot indi-cated the first intron was spliced from GUS pre-mRNA, and the steady-state mRNA levels of GUS with EPI in transgenic tobaccos were higher than that in transgenic tobacco without EPI, which suggested that the first intron of EPSP was a non-translated intron. The first intron (EPI) of rice 5-enolpyruvylshikimate 3-phosphate synthase gene was isolated by PCR from one clone with genomic EPSP synthase gene. Sequence analysis showed that the first intron is 704 bp in length with 36.2% G + C content. To investigate its effect on expres-sion of foreign gene, we inserted the first intron between CaMV35S promoter and b-glucuronidase (GUS) gene. The transient expression results showed that GUS could be expressed effectively with EPI. The GUS activity in transgenic tobacco that that the EPI can greatly enhance the ex-pression level of b-glucuronidase (P <0.01) compared with transgenic tobacco without the first intron, and 3- to 6-fold increase in GUS activity in some transgenic tobaccos. Northern blot indi-cated the first intron was spliced ​​from GUS pre-mRNA, and the steady-state mRNA levels of GUS with EPI in transgenic tobaccos were higher than that in transgenic tobacco without EPI, which suggested that the first intron of EPSP was a non-translate d intron.