Background Biologics have revolutionised the treatment of rheumatoid arthritis (RA). Several types of biologics are used in clinical practice, one of them is the blocker of T cells co-stimulation – abatacept (ABA). The search for predictors of biologics efficacy is an important issue in current rheumatology practice. Objectives To identify predictors of ABA efficacy based on the analysis of various serum biomarkers changes. Methods 44 RA pts with a history of previous DMARDs and biologics failures and 16 healthy donors as controls were included in the study. The majority of pts were females, RF-positive – 80%, anti-CCP-positive – 79,5%, mean age 49.6±13.9 years, median disease duration 21,4;3 years, with high RA activity (mean DAS28=5,2±0,8). Enzyme-linked immunoassay was used to measure serum concentrations of biomarkers IL-1β, IL-6, IL-17AF, TNF-α, VEGF-A, IP-10, YKL-40, MMP3 at baseline and after 6 months of ABA therapy. Disease activity was assessed every 3 months using DAS28. ABA were administered IV according to standard schedule. Results RA pts had significantly increased levels of IL-6 (2.4 [1.1–6,4] vs 0.7 [0,62–1,0] pg/ml, p=0,0002), YKL-40 (9768,4–97, 9 vs 6452,4–107,5 pg/ml, p=0.03), and IP-10 (2112,9–49,8 vs 149,2–15,2 pg/ml, p=0.005) compared to the control group. By the 6-th month ABA significantly reduced the levels of IL-6 up to 1.29 [0,9–2,2] pg/ml, p=0.0006 and IP-10 – to 147,5–28 pg/ml, p=0.007, as well as MMP3 and RF from 30.113–82 to 10 [7.4–55] pg/ml, p=0.0003) and from 218 [9.6–187] to 159 [9.7–155] pg/ml, p=0.02), respectively. There was a significant correlation between the decrease of IL-6 (r=0.5) and IP-10 (r=0,32) levels and decrease of DAS28 scores (p Conclusions ABA therapy led to a significant reduction in concentrations of pro-inflammatory IL-6 and IP-10 cytokines, as well as of MMP3 and RF. The decrease of IL-6 and IP-10 levels significantly correlated with the decrease of RA activity. There was a trend towards more pronounced reduction of disease activity in anti-CCP-positive and anti-MCV-positive pts. High baseline IL-6 and YKL-40 levels were significantly more frequently registered among non-responders. Therefore, anti-MCV-negativity, high baseline levels of IL-6 and YKL-40 could be used as predictors of insufficient ABA efficacy in this category of pts. A small sample of pts is the major limitation of this study, requiring future studies. Disclosure of Interest None declared