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Background and Aim: The intestinal protozoa Giardia lamblia is a parasite frequently involved in human parasitic gastroenteritis throughout the world. Transmission of G. lamblia cysts to human occurs mainly via ingestion of contaminated food and water. The aim of this study was to evaluate Giardia lamblia genetic differences in the Khorramabad City and its surrounding villages by means of PCR and sequencing. Material and Methods: In these study 30 fecal samples positive for Giardia lamblia were collected from the patients in Khorramabad city and its surrounding villages. The samples were fixed in dichromate 5% after filtration. Before DNA extraction, all samples were washed with PBS solution in order to remove dichromate. For determination of genetic differences sequencing on 5 samples was performed. Results: After DNA extraction, amplification of GDH gene from 24 of 30 samples was performed by PCR, successfully. Alignment of the obtained GDH sequences with reference sequences (gene bank) indicated the presence of only one genotype of G. lamblia 5 specimens were identified as G. lamblia assemblage A. Conclusion: Assemblage A was the dominant genotype in Khorramabad City and its surrounding villages. Because of limited number of samples in this study, further studies with higher number of samples are recommended.