Chlortetracycline (CTC), antimicrobial chemical, is widely used to treat disease and protect the health of animals. As CTC is poorly absorbed during digestion, the majority of the bioactive compound or metabolites are excreted in faeces and urine. Toxicogenomics approach was used to examine the toxicological effects of CTC on earthworms (E. fetida). Quantification of gene expression levels encoding antioxidative system and biotransformation enzymes were analyzed in E. fetida. The results showed that GST transcript level was significantly inhibited at 300 mg CTC kg-1, with an approximately a 65% decrease compared to the control. Ferritin and serine were marked by high level transcripts at the lowest concentration and followed by decreasing levels with the increased concentraion. Hsp70 transcript appeared to be disrupted at the lowest concentration. Thus, environmental assessment using these genes expression levels in earthworms might be sensitive and helpful in the early diagnosis of potentially polluted soil.