The frequency and severity of heat stress in livestock production are increasing due to intensive farming practices and rising global temperatures. Due to the lack of sweat glands, poultry are highly susceptible to heat stress, especially in the intestinal tract. Therefore, it is crucial to find environmentally friendly, safe, and effective methods to alleviate heat stress. Probiotics have often been used to mitigate intestinal damage and maintain intestinal function. In this study, the efficacy and mechanism of action of Lactobacillus plantarum 4-2 on oxidative damage and inflammation induced by cyclic heat stress in laying hens were investigated. The results showed that addition of Lactobacillus plantarum 4-2 (≥1 × 10