In this paper we deal with the problem of existence of a smooth solution of the Hamilton-Jacobi-Bellman-Isaacs (HJBI for short) system of equations associated with nonzero-sum stochastic differential games. We consider the problem in unbounded domains either in the case of continuous generators or for discontinuous ones. In each case we show the existence of a smooth solution of the system. As a consequence, we show that the game has smooth Nash payoffs which are given by means of the solution of the HJBI system and the stochastic process which governs the dynamic of the controlled system. This article deals with a nonzero-sum stochastic differential game (NZSDG for short) which we describe hereafter. Let us consider a system, on which intervene two players π 1 and π 2 , whose dynamics is given by a solution of a stochastic differential equation of the following form:where: (i) B := (B t ) t≤T is a Brownian motion ;(ii) u 1 := (u 1t ) t≤T (resp. u 2 := (u 2t ) t≤T ) is a stochastic process with values in U 1 (resp. U 2 ) a compact metric space and adapted w.r.t (F t ) t≤T , the completed natural filtration of B. The process u 1 (resp. u 2 ) is the way by which the first (resp. second) player π 1 (resp. π 2 ) acts on the system ;(iii) f (·) and σ(·) are given functions.The system that one implies could be an asset in the financial market, an economic unit, a factor in the economic or financial spheres, etc. On the other hand, one can consider the differential game with more than two players and this does not rise a major issue, the treatment is the same.The conditional payoff of player π 1 (resp. π 2 ) from t to T , when she implements u 1 (resp. u 2 ), is denoted J 1 t (u 1 , u 2 ) (resp. J 2 t (u 1 , u 2 )) and given by: for i = 1, 2,The functions h 1 , h 2 (resp. g 1 , g 2 ) stand for the intantaneous (resp. terminal) payoffs of the players π 1 , π 2 , respectively. Then the problem of interest is to find a Nash equilibrium point for the game, i.e., a pair of controls of the players (u * 1 , u * 2 ) such that J 1 0 (