Let G be a finite connected simple graph with a vertex set V(G) and an edge set E(G). A total signed dominating function of G is a function f:V(G)∪E(G)→{−1,1}, such that ∑y∈NT[x]f(y)≥1 for all x∈V(G)∪E(G). The total signed domination number of G is the minimum weight of a total signed dominating function on G. In this paper, we prove lower and upper bounds on the total signed domination number of the Cartesian product of two paths, Pm□Pn