Introduction: The serum immunoglobulin free light chain (FLC) assay quantities of free kappa (κ) and lambda (λ) light chains. This assay has prognostic value in plasma cell proliferative disorders. There are limited data on serum FLC in B-cell malignancies. Objectives: The aim of this study was to compare the known prognostic factors in non-Hodgkin’s lymphoma of the type B-cell and Hodgkin disease with an abnormal secretion amount of light chains in these lymphomas. Patients and Methods: The association of pretreatment FLC and FLC ratio (κ:λ) with previously known prognostic factors for lymphoma such as the international prognostic index (IPI) and B symptoms were evaluated in 50 patients with Hodgkin’s and non-Hodgkin’s lymphoma. IPI is a prognostic score given based on the clinical variables including age, disease stage, serum LDH and extra-nodal involvement. Elevated FLC and an abnormal κ:λ ratio was defined based on the previous publications. Results: The prevalence of abnormal FLC ratio was 38% in all patients and 40.9% in patients with diffuse large B-cell lymphoma. Abnormal FLC ratio was significantly associated with IPI (P=0.04) and B symptoms (P=0.02) in both groups of the patients with Hodgkin’s and non-Hodgkin’s lymphoma. The stage of the disease in Hodgkin’s lymphoma patients showed a significant relationship with the abnormal FLC ratio (P=0.04). Presence of the B symptoms in patients with Hodgkin’s lymphoma had a modest but not statistically significant association with the abnormal FLC ratio (P=0.07). Conclusion: Abnormal FLC ratio as a new potent prognostic biomarker has a significant association with IPI which is the most common clinical tool used to predict outcome in lymphoma patients. Since there is a need for developing a reliable and quantitative prognostic biomarker for lymphoma, evaluation of the independent effect of the abnormal serum FLC ratio is suggested to be considered in future prospective studies. The result of these studies will also be useful for nephrologists, while serum immunoglobulin FLC is capable to damage kidney.