Serum levels of inflammatory factors, such as C3, C4, C-reactive protein (CRP), immunoglobulin (Ig) G, IgA, and IgM, in patients with Alzheimer's disease (AD) and their correlation with cognitive function remain unexplored.To investigate the expression of serum inflammatory factors in patients with AD and its correlation with cognitive function.Serum levels of C3, C4, CRP, IgG, IgA, and IgM in 200 patients with AD (mild, moderate, and severe) and those in 174 normal controls were assessed. Spearman's rank correlation analysis was used to explore the relationships among biomarker levels, cognitive function, and activities of daily living (ADL).Among these inflammatory factors, C3 and CRP levels were significantly lower, and IgG and IgA levels were significantly higher in the AD group than in the control group (p <  0.05). There were no significant differences in C4 and IgM levels between the two groups (p >  0.05). In all participants, CRP level was positively correlated with the Mini-Mental State Examination and Montreal Cognitive Assessment scores (p <  0.05). In the AD group, IgA level was negatively associated with ADL scores (p <  0.05). No significant correlation was detected between the other factors and different cognitive scores (p >  0.05).Inflammatory factors C3, CRP, IgG, and IgA have the potential to serve as biomarkers for AD. Furthermore, serum IgA was not only correlated with AD but also with ADL. These results support the hypothesis that inflammation is involved in the occurrence and development of AD.