Glutathione S-transferases are multifunctional enzymes for the cellular defense against xenobiotics and provide protection for organism. In this study, the inhibition effects of some antibiotics were investigated against GST obtained from albino-rats kidney, liver, and heart tissues. Ninety-six albino-rats were randomly divided into 16 groups (n:6). The first four groups were control groups that were administrated blank enjection and decapitated at 1-7 h. The other groups were administrated the antibiotics. In all tissues, GST activity was increased in antibiotics groups at 1st and 3rd hours compared to control groups, while it began to fall at 5th and 7th hours (p < .05). In kidney tissues, it was lower than the same control group the cefuroxime and cefoperazone groups at 7th hours (p < .05). In addition, almost all antibiotic groups of kidney tissues had higher GST activity at all hours than those of control groups, but it was higher only at 5th hours in heart tissues (p < .05).