This study was conducted in order to assess the effect of inoculation of soybean (Glycine max L.) seeds with Trichoderma asperellum, followed by mites (Tetra nychus urticae) exposure on lipid peroxidation (LP) process and the activity of antioxidant enzymes. T. urticae is an occasional pest of soybean that causes biotic stress. Biotic stress leads to overproduction of reactive oxygen species (ROS) which may cause damage to vital biomolecules. Enzymatic antioxidant defense systems protect plants against oxidative stress. T. as perellum is commonly used as biocontrol agent against plant pathogens. It has been suggested that previous inoculation of seeds with T. asperellum may cause induced resistance against biotic stress. The aim of this study was to determine LP intensity and antioxidant enzymes activity in inoculated and non-inoculated soybean seedlings with and without exposure to mites. Noticeably higher LP intensity was detected in non-inoculated group treated with mites compared to control group. Inoculated soybean seedlings treated with mites had lower LP intensity compared to non-inoculated group. Also, it has been noticed that inoculation with Trichoderma asperellum itself, produced mild stress in plants. In addition, positive correlation between enzymes activity and LP was noticed. The level of oxidative stress in plants was followed by the change of LP intensity. According to results obtained, it was concluded that the greatest oxidative stress occurred in non-inoculated group treated with mites and that inoculation successfully reduced oxidative stress. The results indicate that inoculation of soybean seeds with T. asperellum improves resistance of soybean seedlings against mites attack.