Pneumonia is a common infection in elderly patients. We explored the correlations of serum interleukin-6 (IL-6) and serum ferritin (SF) levels with immune function/disease severity in elderly pneumonia patients. Subjects were allocated into the mild pneumonia (MP), severe pneumonia (SP), and normal groups, with their age/sex/body mass index/ disease course and severity/blood pressure/comorbidities/medications/prealbumin (PA)/albumin (ALB)/C-reactive protein (CRP)/procalcitonin (PCT)/smoking status documented. The disease severity was evaluated by pneumonia severity index (PSI). T helper 17 (Th17)/regulatory T (Treg) cell ratios and IL-6/SF/immunoglobulin G (IgG)/Th17 cytokine (IL-21)/Treg cytokine (IL-10)/PA/ALB levels were assessed. The correlations between these indexes/independent risk factors in elderly patients with severe pneumonia were evaluated. There were differences in smoking and CRP/PCT/ALB/PA levels among the three groups, but only CRP/ALB were different between the MP/SP groups. Pneumonia patients exhibited up-regulated Th17 cell ratio and serum IL-6/SF/IL-21/IL-10/IgG levels, down-regulated Treg cell ratio, and greater differences were noted in severe cases. Serum IL-6/SF levels were positively correlated with disease severity, immune function, and IL-21/IL-10/IgG levels. Collectively, serum IL-6 and SF levels in elderly pneumonia patients were conspicuously positively correlated with disease severity and IL-21/IL-10/IgG levels. CRP, ALB, IL-6 and SF levels were independent risk factors for severe pneumonia in elderly patients.