Objective. Evaluation of the relationship between laboratory rabbits thoracic aorta strength under uniaxial stretching and serum magnesium level against background of ciprofloxacin and levofloxacin. Methods. 20 rabbits "Soviet chinchilla" at the age of 5 months were randomized into three groups: group 1 (6 animals received placebo for 14 days), group 2 (7 animals received ciprofloxacin 150 mg/kg for 14 days), group 3 (7 animals received levofloxacin 150 mg/kg for 14 days). On the 15th day, the animals were withdrawn from the experiment, thoracic aorta samples were subjected to mechanical test for uniaxial tension. Sample tensile strength, maximum deformation, elasticity modulus, and destruction work were determined. Serum magnesium level was analyzed. Results. Ciprofloxacin use did not change aorta strength. In levofloxacin group, there was significant decrease in aorta destruction work (21.1±10.2 mJ versus 46.6±17.4 mJ in control group, p = 0.011). Serum magnesium levels did not change with both of fluoroquinolones (p > 0.050 for both drugs). The dependence of magnesium concentration and aortic strength was found only in the control group; it was not detected when using fluoroquinolones. Conclusion. Levofloxacin showed the most dramatic damaging effect on thoracic aortic wall strength properties. Studied drugs did not reduce serum magnesium levels. Fluoroquinolones, most probably, contribute to the magnesium redistribution from tissues to blood, resulting in a normal content of Mg2+ in serum, but there is its metabolism violation in the aortic wall.