Abstract: The extract of Radix Paeonia rubra, a common traditional Chinese drug was shown to inhibit platelet aggragation and oxidative phosphorylation while increasing fluidity of rat liver mitochondria. This paper reports the effects of propyl gallic acid, one component isolated from Radix Paeonia, on rat liver mitochondrial swelling and malondialdehyde (MDA) formation.Experiments on the formation MD and swelling of rat liver mitochondria induced by Fe²⁺ (5 μM)and vit C (0.1 mM) with or without the drug was carried out in vitro. In order to study the protectiye effects of drug against the damage of the mitochondria. The results show-that propyl gallic acid inhibited the swelling of mitochondrta andMDA formation. Fe²⁺ and vit C were also shown to reduce ANS fluorescence in mitochondrial suspension. It is inferred that the cross reaction of MDA with biological macromolecules and the decrease of surface potential of mitochondrial membrane are factors that induced damage to the function of mitochondria. This compound was shown to be unable to inhibit MDA damage to the mitochondria. However, the anti-oxidative and antiswelling action of the drug on mitochondria may be associated with the Pharmacological effects of Radix Paeonia rubra.