Objective: The combination of arterial hypertension (AH) with abdominal obesity (AO) significantly increases the severity of hypertension and accelerates the development of hypertension-mediated organ damage, in particular, left ventricular hypertrophy (LVH). MicroRNAs are small non-coding RNA molecules that are involved in the regulation of post-transcriptional gene expression. A number of experimental studies have revealed the antihypertensive, antihypertrophic and antifibrosing properties of microRNA-21-3p. The goal is to study the plasma levels of microRNA-21-3p in hypertensive patients with normal body weight (NBW) and with abdominal obesity (AO). Design and method: 27 patients (16 men) with stage 2-3 hypertension (13 with NBW and 14 with stage II AO) aged from 42 to 60 years were examined. The control group consisted of 12 practically healthy individuals. All patients underwent general clinical laboratory and instrumental examination. Circulating plasma microRNA-133a levels were obtained by polymerase chain reaction using the CFX96 Touch System, “TaqMan microRNA Assay” and “TaqMan® Universal PCR Master Mix” reagent kits. Results: A significant decrease in the levels of micoRNA-21-3p in the blood plasma was established in the whole group of patients with hypertension (with NBW and with AO) (1.43±0.08), p<0.05) in comparison with practically healthy individuals (3.24 ±0.07). At the same time, the levels of this miRNA in the blood plasma of patients with hypertension and AO (1.13±0.06) were significantly lower (p<0.05) than in patients with hypertension and NBW (1.67±0.07). A correlation analysis revealed negative correlations between the levels of micoRNA-21-3p in the blood plasma and the levels of “office” systolic blood pressure (R=-0.44; p=0.04), as well as the left ventricular myocardial mass index (LVMMI) (R= -0.38; p=0.03) in the whole group of patients with AH (with NBW and AO). Conclusions: The results of this study may indicate the presence of a significant deficiency in the production of mircRNA-21-3p in patients with hypertension, especially when it is combined with AO, as well as the involvement of this miRNA in the mechanisms of progression of hypertension and the development of LVH.