It is an object of the present invention to provide hydrotalcite which can inhibit a white discoloration by water of a polyolefin film for agricultural uses, a blooming to the surface of a vinyl chloride resin film, a reduction in electric resistance in the case of using the hydrotalcite as a stabilizer of a vinyl chloride resin for covering wires, the occurrence of die drool in the case of using the hydrotalcite as a neutralizer of an acid catalyst residue in a polyolefin resin or a copolymer thereof, and coloring (yellowing) in extrusion in preparing pellets and can be suitably used as a resin additive, a method of producing the same and a synthetic resin composition containing the same.Hydrotalcite expressed by the following formula (1); [(Mg).sub.x(Zn).sub.y].sub.1-z(Al).sub.z(OH).sub.2(A.sup.n-).sub.z/n.mH.s- ub.2O (1) in the formula A.sup.n- represents an anion having a valence of n, and x, y, z and m are values which satisfy the following expressions, 0.5.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.0.5, x+y=1, 0.1.ltoreq.z.ltoreq.0.5, 0.ltoreq.m<1, and the hydrotalcite has a sodium content of 100 ppm or less and is used as a resin additive.