A dominator coloring of a graph G is a proper coloring of G with the additional property that every vertex dominates an entire color class. The dominator chromatic number \(\chi _d(G)\) of G is the minimum number of colors among all dominator colorings of G. In this paper, we determine the dominator chromatic numbers of Cartesian product graphs \(P_2 \square P_n\) and \(P_2 \square C_n\).