We present a patient with beta-thalassemia minor diagnosed on the basis of the incidental findings of marked hypochromic and microcytic erythrocytosis. Hemoglobin analysis revealed increased hemoglobin (Hb) A2 levels and decreased beta/alpha synthesis ratio in both the propositus and his mother. Further molecular studies identified a single base substitution of TCA to TAA within codon 35 in heterozygous state, which creates a premature terminator resulting in a defect of effective beta globin synthesis. This is the first report of beta-thalassemia due to a nonsense mutation at codon 35 of beta-thalassemia gene in the Japanese population.