A twelve-piece tangram puzzle set is disclosed. The twelve-piece tangram puzzle set includes twelve pieces, the twelve pieces being formed in such a manner that an equilateral triangle is formed as a basic frame and is bisected into right-angled triangles by a first cutting line, second cutting lines, horizontal cutting lines and vertical cutting lines, and equiangular cutting lines so as to be divided into respective pieces 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, such that triangles (pieces 1, 3, 7, 9, 11) are symmetrical to triangles (pieces 2, 4, 8, 10, 12), and a trapezoidal quadrangle (piece 5) is symmetrical to a trapezoidal quadrangle (piece 6) based on the first cutting line.