Abstract: Serum β_2-microglobulin (β_2-MG) was tested by radioimmunoassay in 149 donors' and 54 healthy volunteers' blood. The results were 203±33.0 nmol/1 and 176 ± 26.2 nmol/1, respectively. There was significant difference statistically between them (P<0.001). The results showed that the longer the history of blood donor or the shorter the interval of blood donating, the higher the β_2-MG content. In order to increase the quality of donated blood and to keep the health of blood donor, it is suggested that the high content of serum β_2-MG be the indicator of too frequent blood donating. The results also showed that the content of β_2-MG in donor's blood is not a normal reference value.