Abstarct: Let G be a graph with vertex set V (G) and edge set E(G). A set Z of vertices of a graph G is a zero forcing set of G if iteratvely adding to Z vertices form V (G) nZ that are the unique neighbor in V (G) n Z of some vertex in Z, results in the entire vertex set V (G). The zero forcing number Z(G) of G is the minimum cardinality of a zero forcing set of G, and denoted by Z(G). We study lower bounds on the forcing number of graphs in terms of its minimum degree and girth,where the girth g of a graph is the length of a shortest cycle in the graph. For the graph G with minimum degree δ ≥ 2 and girth g ≥ 3, we will show that Z(G) ≥ δ + (δ - 2) (g - 3)