Six Giardia lamblia strains (4 from Egypt, one from the USA and one from Sudan) were used to study the phenotypic and genotypic variation in some Egyptian G. lamblia strains compared to other G. lamblia strains, which may be responsible for the difference in their behavioral characteristics. By using SDS-PAGE for antigenic study, E1 strain appeared different from the rest of the strains with two bands; one at 121 Kda and the other at 34 Kda which were not present in other strains, while bands at 130 and 43 Kda were present in all strains but absent in E1 strain. Another difference between E1 strain and the rest of the strains was obtained by CAE, using PGM enzyme where E1 strain gave a different zymodeme than the other strains. Based on the computerized RAPD- PCR analysis, 4 rapdemes were identified; rapdeme 1 contained E1 strain, rapdeme 2 contained E2, E3 and E4 isolates, rapdeme 3 contained Sudan strain and rapdeme 4 contained USA strain. In conclusion this study revealed diversity between G. lamblia strains especially E1 strain which showed unique characters.