Abstract: Objective To trace the infection sources of three dengue virus type 1 isolates found in Guangdong province, namely GD05/99, GD14/97 and GD23/95. Methods According to the genomes of dengue virus type 1 S275 strain, a pair of primers was designed for amplification of the structural protein E gene of the isolated dengue virus type 1 strains by reverse transcriptase-PCR. The amplified gene fragment was then cloned into pMD18-T vector and sequenced. Results GD14/97 and GD05/99 shared a high nucleotide homology with Cambodia (98% and 99% respectively) and may belong to the same genotype. GD23/95 had a 95% nucleotide homology with A88, higher than that with other strains. GD23\95 and A88 may belong to another genotype. Conclusion The dengue fever outbreak in Guangdong during 1999, 1997, and 1995 may originate from the viruses from different countries.