Abstract: Objective To investigate the changes of multiple organ function and inflammatory factors in the aged rats with systemic inflammatory response syndrome (SIRS) model induced by zymosan.Methods By intraperitoneal injection of Zym-paraffin suspension were prepared SIRS models of adult and aged SD rats. According to different injected doses were set up groups of 750 mg/kg, 500 mg/kg, 250 mg/kg, 125 mg/kg model group, and a blank control group. The success of the model building was determined by observation on the body temperature,respiratory rate,white blood cell count, and heart rate before and after the model was built. Arterial blood gas analysis was made in blank control group and model groups, including:potential of hydtrogen(pH),partial pressure of carbon dioxide(PaCO₂),partial pressure of oxygen(PaO₂), oxygen saturation(SaO₂),and peripheral blood biochemical indexes were detected, including:alanine aminotransferase(ALT),aspartate aminotransferase (AST),creatine kinase(CK),lactate dehydrogenase(LDH),creatinine(Cr), and tumor necrosis factor-α(TNF-α),interleukin-1β(IL-1β),interleukin-6(IL-6),interleukin-10(IL-10). Measurement data analysis was done by using t test.Results As the adult 500 mg/kg group and 250 mg/kg group were compared with the adult blank control group,the differences found between them in the results of blood gas analysis, serum test indexes and inflammatory factors were statistically significant (P<0.01,P<0.05). The results of blood gas analysis, serum test index and inflammatory factor in adult 125 mg/kg group were similar to those in adult blank control group and there were no statistically significant differences(P>0.05). As the aged 500 mg/kg group,250 mg/kg group,125 mg/kg groupand were compared with the aged blank control group,the differences found between in the results of blood gas analysis, serum test index and inflammatory factor were statistically significant (P<0.01,P<0.01,P<0.05).As the aged rats were compared with the samedose adult rats (500 mg/kg group, 250 mg/kg group, 125 mg/kg group),the differences found between them in the results of blood gas analysis, serum test index and inflammatory factor were statistically significant(P<0.01,P<0.01,P<0.01).Conclusion The SIRS model of 500 mg/kg in adult rats with intraperitoneal injection of Zym-paraffin suspension was better than models of other dosage, and the dose of 250 mg/kg preferred for the SIRS model of the aged rats. With the same dose of zymosan, the function of each organ in the elderly group were not as good as that in the adult rats,and the levels of inflammatory factors in the elderly group were higher.