The dynamics of a bubble in a low-viscosity liquid is considered. The equation of dynamics of small perturbations with allowance for viscosity effects is determined.Let us consider a bubble with a variable radius in a low-viscosity liquid. Let the shape of the bubble surface S be close to spherical. The goal of the present paper is to derive the equation of dynamics of surface perturbations.Let us introduce a spherical coordinate system (r, θ, ϕ) with the origin in the sphere center. The expression for the bubble-surface radius r 0 includes a small perturbation proportional to the spherical harmonic Y n :Here, R is the radius of a sphere with an equivalent volume and a is the perturbation amplitude; the integral of Y 2 n over a unit sphere is assumed to be equal to unity. In what follows, the argument t at the functions R, r 1 , and a is omitted. It follows from the expression for the bubble volume V = (4/3)πR 3 that the value of the variable isThe unperturbed velocity field is potential. Let the perturbation of the velocity field around the bubble be also close to potential. This is possible if the product of the kinematic viscosity ν and the characteristic time τ is small: ντ l 2 (l = πR/n is the characteristic distance). The velocity potential v = ∇Φ is found by solving the Neumann problemin an approximate form:Here, the coefficient at 1/r is valid with accuracy to smallṘa 3 /R 2 andȧa 2 /R. To describe the perturbation dynamics, we use an energetic approach similar to that used in [1] to describe the dynamics of a system of bubbles in a low-viscosity liquid. The generalized forces in the Lagrange equations can be expressed in terms of the rate of energy dissipation E in the potential velocity field:The generalized coordinates are q 1 = a and q 2 = R. The Lagrange function is L = T f − σS (T f is the kinetic energy of the liquid and σ is the surface tension). The kinetic energy and the dissipation rate are determined by the formulasTyumen'