In this paper, we obtain generating functions of three-variable Chebyshev polynomials (of the first as well as of the second type) associated with the root system of the A 3 Lie algebra. Bibliography: 21 titles.To Petr Petrovich Kulish on the occasion of his 70th birthday 1. The aim of the present paper is to obtain generating functions of Chebyshev polynomials in three variables. Chebyshev polynomials in several variables associated with the root systems of simple Lie algebras were intensively studied in the last decades [1][2][3][4][5][6]. Such polynomials are applied in various areas of mathematics, as well as in physics. Examples of such applications with references can be found in the papers [7][8][9][10][11][12][13][14][15][16].Multivariate Chebyshev polynomials are natural generalizations of the classical ones. The classical Chebyshev polynomials T n (x) of the first kind are defined by the following formula (see, for example, [17]):( 1 ) they satisfy the following three-term recurrence relation:The classical Chebyshev polynomials U n (x) of the second kind are defined by the formulawhich is different from (1), but they satisfy the same recurrence relation (2). The initial conditions for the above polynomials are T 0 (x) = 1, T 1 (x) = x, U 0 (x) = 1, and U 1 (x) = 2x;( 3 ) together with the recurrence relation (2), they determine the polynomials uniquely without reference to (1) and (2). It is known that the function cos nφ can be treated as the invariant mean of the exponential function over the Weyl group of the A 1 algebra root system:Transition to a function that is the invariant mean over the Weyl group W of another root system leads us to generalization of the classical Chebyshev polynomials to polynomials in several variables [1][2][3][4]. Let us shortly recall the way in which such W -invariant functions can be constructed. Let R(L) be a reduced root system of any simple Lie algebra L. Such a system is a set of vectors in the d-dimensional Euclidean space E d supplied with scalar product (., .). The system R is uniquely determined by the base of simple roots α i , i = 1, . . . , d, and by a finite group W (R) which is generated by base reflections. This group is called the Weyl group.