In order to study "tailed nuclei" (TN) in peripheral blood smears from irradiated Chernobyl liquidators, human peripheral blood lymphocytes from irradiated Chernobyl liquidators as experiment group were selected to observe under microscope and record different TN pattern in routine Giemsa dyeing method with 500 cells. Result shows that TN percent in control group is 0 to 1.0% while the TN percent in the irradiated group is higher (most is 3.2%). The frequency of appearance of lymphocytes with TN in a group of Chernobyl liquidators is significantly higher than that in control groups (,p,<,0.01). Abnormalities of the TN type in irradiated lymphocytes may be from breakdown of chromosome bridges formed in dicentrics. The TN could be considered as a possible marker involved in radiation damage of biological tissue.