Diethyl phthalate [DEP] is used in pharmaceutical coating, cosmetics and plastic forms to wrap foods. There is health concern associated with the exposure to certain phthalate esters because they belong to a class of compounds referred to as peroxisome proliferators which have been shown to increase the incidence of liver tumours in rats. In this work we have different body systems through the assessment of studied the effect of DEP on the functions relevant biochemical parameters. The work was carried out on twenty adult male albino rats divided into two groups of ten rats each, group I: animals were maintained as control on normal diet. In group Il animals received [200 mg/Kg body weight / day] diethyl phthalate in water for a period of 30 days. At the end of the treatment period, specimens of serum were collected and livers were excised for determination of some serum enzymes and other biochemical parameters. It was observed that serum levels of aspartate aminotransferase [AST], alanine aminotransferase [ALT], alkaline phosphatase [ALP] and gamma-glutamyl transferase [GGT] were increased significantly in DEP treated rats, this was coupled with significant decreases in liver AST, ALT, and ALP levels. The serum and liver acid phosphatase [ACP] showed significant increases in DEP treated rats compared with controls. On the other hand, liver glucose-6-phosphatase enzyme showed a significant decrease in DEP treated rats, while there was a significant increase in hepatic lipid peroxidation as manifest by increase in malondialdehyde [MDA] concentration. There was a significant increase in liver glycogen levels, liver carnitine acetyl transferase and liver triglycerides in DEP treated rats. On the contrary serum triglycerides levels showed a significant decrease. From the previous results it could be concluded that DEP is capable of inducing hepatocellular toxic effect manifested by the alterations in activity of some enzymes in the liver and serum. There was also impairment in metabolic processes such as glycogen and triglyceride storage in the liver due to the lipophilic nature of DEP. Due to the toxic effects induced by long term exposure to phthalates, it would be advisable to replace polyvinylchloride [PVC] plasticizers especially if they come in contact with high risk groups with better quality materials.