The macrolide antibiotic tilmicosin is known to induce cardiotoxic effect when administered at large doses. In this work, the effects of tilmicosin were evaluated with respect to alterations in total sialic acid, malondialdehyde and glutathione content of the hem liver, kidney and lung tissues after single subcutaneous injection of 75 mg/kg tilmicosin with or without L-carnitine (500 mg/kg for 5 days daily via s.c. route) in BALB/c mice. L-carnitine is a co-factor serving in the mitochondrial beta-oxidation of long chain fatty acids, and it was reported to be protective in several types of toxicity cases probably via multi-factorial mechanisms. Twenty eight mice were divided into 4 groups including group 1 (control), group 2 (L-camitine), group 3 (tilmicosin) and group 4 (tilmicosin plus L-camitine). Following the administration of treatments, tissue samples were collected, and the samples were assayed for malondialdehyde, glutathione and total-sialic acid content. Mice receiving tilmicosin treatment alone had significantly higher malondialdehyde and total sialic acid concentrations (except for MDA of lungs) but lower glutathione concentration in selected tissues compared to those of the control, group 2 (Carnitine only) and group 4 (L-camitine plus tilmicosin) (p < 0.05). However, no significant difference was found associated with the assayed indicators between the control and mice treated with L-carnitine plus tilmicosin. These results suggest that tilmicosin may cause oxidative stress in the heart, liver, lung and kidneys, but the adverse effects could be attenuated by L-carnitine administration.