Metabolic changes during kidney and liver disease can induce increased production of oxygen radicals that play an important role in the progression of kidney and liver damage and in the appearance of important comorbidities. In the study reported here, the effect of alpha-lipoic acid (ALA) on the chemiluminescence (CL) and TBARS determination of microsomes isolated from rat kidney and liver was analyzed. Oxidative stress in microsomes was induced by subjecting samples (1 mg of protein) to an ascorbate-Fe++-dependent (0.4 mM)-Fe++ (2.15 μM) prooxidant system at 37 °C for 120 min. Oxidative damage was quantified by two methods, TBARS and CL: CL was determined using a Packard 1900 TR liquid scintillation counter (Meriden CT, USA). CL was expressed as cpm (counts per minute) was read every 10 minutes to establish the course of peroxidation as a function of time. Likewise, the total value of cpm (sum of the readings) was used to compare the inhibitory effect of ALA using different concentrations corresponding to 0.05; 0.15 and 0.25 μg of ALA per mg of microsomal protein. Controls were run simultaneously without the addition of ascorbate-Fe++. It was observed that the CL was lower in the kidney and liver microsomes obtained from the ALA group than in the control group (without ALA). In addition, -ALA was found to be concentration-dependent (0.05, 0.15 and 0.25 μg of ALA per mg of solution) reduced in CL, measured as total cpm. After that it was done the determination of lipid peroxidation products (Thiobarbituric Acid Reactive Substances—TBARS). TBARS were measured in the microsomal samples. Lipoperoxidation inhibition depended on the concentration of ALA in the incubation mixture. The results show that for all the concentrations tested, a protective effect on the induced oxidative damage was found. CL and TBARS level analyzes indicate that ALA may act as an antioxidant protecting rat kidney and liver microsomes from lipoperoxidative damage.