This experiment was conducted to investigate the effects of Macleaya cordata (MC) extracts on stress parameters and mRNA expressions of immunoglobulin G (IgG) and superoxide dismutase (SOD) of cells challenged by lipopolysaccharide (LPS) in pigs. Embryo fibroblasts cells on the back of pigs were selected as the experimental material. The experiment was carried on normal cells and the stress model challenged by LPS. A basal culture medium was used in the control group, the basal culture medium supplemented with 50 μg/mL oxytetracycline was used in oxytetracycline group (negative control), and the basal culture medium supplemented with 50, 100 and 150 ng/mL MC extracts were used in MC groups, respectively. Contents of IgG, lysozyme (LSZ), nitric oxide (NO) and nitric oxide synthase (NOS), lactate dehydrogenase (LDH) activity, as while as mRNA expression levels of IgG and SOD were determined. The results showed as follows: 1) contents of IgG, NO, NOS and LSZ in MC group were all significantly higher than those in the control group (P<0.01), and contents of IgG and LSZ in oxytetracycline group were significantly higher than those in the control group (P<0.01). 2) For stressed and normal cells, IgG mRNA expression level in MC groups was significantly higher than that in the control group and oxytetracycline group (P<0.01), and 50 and 150 ng/mL MC groups were significantly higher than 150 ng/mL MC group (P<0.01). IgG mRNA expression level in oxytetracycline group was significantly higher than that in the control group (P<0.01). IgG mRNA expression level of stressed cells was significantly higher than that of normal cells in 100 ng/mL MC group (P<0.01). 3) For stressed and normal cells, compared with the control group, supplementation of 50, 100 and 150 ng/mL MC extracts significantly increased SOD mRNA expression level (P<0.01). SOD expression level in oxytetracycline group was significantly higher than that in the control group and MC group (P<0.01). SOD mRNA expression level of stressed cells was significantly higher that of normal cells (P<0.01). In conclusion, MC extracts can increase contents of IgG, NO, NOS and LSZ of stressed cells, as well as IgG and SOD mRNA expression levels both in stressed and normal cells. The effects of MC are better than those of oxytetracycline, and the optimal level is 50 to 100 ng/mL.