Background: Chronic myeloproliferative neoplasms are characterized by clonal hematopoiesis and persistent inflammatory reaction. In this study, the clinical significance and prognostic impact of several inflammatory markers were evaluated in patients with BCR/ABL-negative myeloproliferative malignancies. Methods: Serum levels of interleukin-8 (IL-8) and lymphoid-associated activation markers - soluble interleukin-2 receptor (sIL-2R) and immunoglobulin-free light chains (FLC) - were evaluated in patients with primary myelofibrosis (MF), post-polycythemia vera MF, and post-essential thrombocythemia MF, and compared with the levels in healthy donors. Results: In 57 MF patients, sIL-2R excess correlated with transfusion-dependent anemia (p = 0.03) and splenomegaly (p = 0.02). There were no statistically significant correlations between sIL-2R and IL-8 levels, but the plasma concentration of κ-FLC positively correlated with the IL-8 level (p = 0.027). In univariate analysis, increased levels of IL-8 (p = 0.016) and sIL-2R (p = 0.010) significantly reduced 1-year overall survival. Only elevated sIL-2R rate retained significance (p = 0.02) in multivariate analysis when Dynamic International Prognostic Scoring System plus (DIPSSplus) risk stratification was added. Conclusion: We observed an association between FLC and proinflammatory cytokine hyperexpression. Serum cytokine levels and FLC might be a promising approach to predicting and monitoring treatment response in MF patients.