The association between gut microbiota and circulating zonulin level, a marker of intestinal permeability, has not been studied yet. The aim of the study is the assessment of plasma zonulin, haptoglobin and proinflammatory cytokines (TNF-αand IL-6) levels in relation to composition of gut microbiota in obese and normal weight subjects. Circulating inflammation markers, such as TNF-α, sTNFR1, sTNFR2, IL-6, zonulin, and haptoglobin levels were measured and semiquantitative analysis of gut microbiota composition was carried out in 50 obese and 30 normal weight subjects without concomitant diseases. Higher circulating zonulin, TNF-α, sTNFR1, sTNFR2, and IL-6 levels were found in the obese subjects. Plasma zonulin level correlated positively with age (,), body mass (,), BMI (,), fat mass and fat percentage (,and,, resp.). Positive correlations between bacterial colony count and sTNFR1 (,) and plasma zonulin (,) but not haptoglobin levels were found. Additionally, plasma zonulin level was proportional to daily energy intake (,) and serum glucose concentration (,) and inversely proportional to diet protein percentage (,). Gut microbiota-related systemic microinflammation in the obese is reflected by circulating zonulin level, a potential marker of interstitial permeability.