Objective Systemic lupus erythematosus (SLE) is a multisystem inflammatory disease characterized by the production of various autoantibodies. The aim of this study was to investigate the presence of anti–ficolin‐2 antibodies in SLE patients and to evaluate the association between the levels of these autoantibodies, clinical manifestations, and disease activity. Methods This is a comparative study using a cohort of 165 SLE patients and 48 healthy subjects. SLE patients were further divided into 2 groups (low disease activity SLE Disease Activity Index (SLEDAI) score ≤4, n = 88 and high disease activity SLEDAI score >4, n = 77). Clinical manifestations were defined according to the physician in charge. Active lupus nephritis (LN) was documented by kidney biopsy. Detection of anti–ficolin‐2 antibodies was performed by enzyme‐linked immunosorbent assay. Results Levels of anti–ficolin‐2 autoantibodies were significantly higher in SLE patients as compared to healthy subjects and associated with SLEDAI score. They were found to be positive in 61 of 165 SLE patients (37%). The presence of anti–ficolin‐2 antibodies was significantly related only to renal involvement, with a very high prevalence (86%) of anti–ficolin‐2 antibodies in SLE patients with active LN. Patients with active proliferative LN had significantly more positive anti–ficolin‐2 antibodies than those with nonproliferative LN. The combination of anti–ficolin‐2, anti–ficolin‐3, and anti‐C1q demonstrated a very high specificity (98%) for the diagnosis of active LN. Conclusion Our results support the usefulness of anti–ficolin‐2 as a complementary serologic biomarker for the diagnosis of active lupus with renal manifestations.