Triangular isoparametirc element,formed by collapsing one side of the cubic isoparametric quadrilateral element into crack tip and placing the two nodes of each side of the crack tip at the positions of 1/9 and 4/9 side length measured from the tip,are shown to embody the 1/√r singu- larity of elastic fracture mechanics and the 1/r singularity of perfect plasticity. The proposed elements are applied to center crack and edge crack problems,and the finite element results are compared with theoretical results to demonstrate the accuracy of the singular element.