Clinical heterogeneity is often due to genetic heterogeneity. One mechanism by which different mutations can produce a phenotypic variation). Beta-thalassemia is mainly caused by a large number of mutations of the gene for beta-globin. The objective of this study is to correlate molecular lesions and clinical signs in children with beta-thalassemia homozygous. We carried out the molecular genetics of beta globin gene by the method of mini sequencing using Snapshot ™ kit (Applied Biosystems) in search of the mutation codon 39 (C>T) (HBB: c.118C>T) and we studied haematological parameters by statistical method using the test "t" of Student for comparing the means of the samples. The peripheral blood smear examination was done from the slides stained in Wright stains. The results obtained have shown that beta-thalassemia homozygous children with severe anemia over 30 ± 0.9 g/L of total Hb with microcytosis of 60,80 ± 2.014 fl, hypochromia 18.47 ± 0.6023 pg and the number of red blood cells is 3.220 ± 0.2778 (1012/L). In addition, a significantly secondary thrombocytosis and leukocytosis were reported in patients. Thus the electrophoresis of hemoglobin exhibits a high Hb F (55 to 82%). The peripheral smear examination revealed many red cell abnormalities in the blood. In this study, we used the mini sequencing assay as a rapid screening procedure to identify the severe codon 39 (C>T) mutation in the HBB gene. Phenotype of beta thalassemia major is characterized with various hematological parameters.