High-dose radiation is deleterious to cells or tissues. However, the health risks of exposure to low-dose radiation remain unclear. The present study aimed to investigate the biological responses of low-dose gamma-ray exposure to normal red blood cells (RBCs) and erythroleukemia (K562 and K562/Dox) cancer cells. Cells were given a low dose of 0.03, 0.05 and 0.1 mGy of Cs gamma-rays (at a dose rate of 0.001 Gy/min) under conditions. Cells exposed to 0 Gy served as controls. Hemolysis and reactive oxygen species (ROS) were measured in exposed RBCs following exposure to low-dose gamma-rays. In addition, complete blood count (CBC) parameters were determined in irradiated whole blood. For irradiated K562 and K562/Dox cancer cells, ROS and mitochondrial activity were measured at 0, 30, 60 and 120 post-irradiation times. The results showed no change in the percentage of ROS and hemolysis in irradiated RBCs. The data indicated no perturbation in the CBC parameters in irradiated whole blood. By contrast, statistically significant dose-dependent increases in the percentage of ROS and decreases in the mitochondrial activity in the K562 and K562/Dox cancer cells were observed from 0 min up to 120 min post-irradiation. These findings concluded that there were differences in biological responses in normal cells (RBCs) and cancer cells (K562 and K562/Dox) to low-dose gamma-rays when cells were irradiated under conditions.