The influence of increased medium viscosity on the activity of myosin Ca2+-ATPase has been studied in 28, 45 and 60% water-sucrose solutions at 25 degrees C. In the wide range of viscosities (10 divided by 430 mp) the rate constant of ATP hydrolysis displays the negative power-law dependence on solution viscosity with an index approximately -0,5. The obtained data confirm an idea about the existence of direct connection between the low-frequency liquid relaxations and structural dynamics of proteins and enzymes.