Beta thalassemia is the  most common autosomal recessive disorder. The present study reports a rare β globin gene mutation, HBB: c.180G>A: codon 59 (AAG/AAA), in a patient from Gilan province, northern Iran. Nucleotide sequencing of amplified DNA belonging to a 35 years old man presenting mild hypochromia revealed a synonymous mutation due to a G>A conversion at the third position of codon 59 of the beta globin gene. The haplotype combination of 2 restriction enzyme sites in beta globin cluster was determined for this mutation. To our knowledge, this is the first article reporting a synonymous mutation  at codon 59 (G>A) among the Iranian population highlighting once again the high heterogeneity of this population.