Various nucleon-pair approximations of the nuclear shell model have been developed in the last sixty years.Important examples of nucleon-pair approximations include the seniority scheme or quasispin scheme [1,2],the broken pair approximation [3],the Ginocchio model [4].There have been many studies of the microscopic foundation of the interacting boson models [5],in which the validity of pair approximation has been examined in many cases [6,7].In most of pair approximations the isospin,however,is not a good quantum number.If one studies pair approximation of nuclei with both valence protons and neutrons in the same shell,pair approximation with isospin symmetry must be developed.In this talk I shall present our formulation of pair approximation with isospin symmetry.I shall exemplify our approach by calculating low-lying states of 92Pd,in which spin-aligned proton-neutron pair mode was thought to be important [8-10].The configurations constructed by (g9/2)2 spin-aligned isoscalar pairs occupy over 80% of yrast state wave functions.This is a joint work with Yu-Min Zhao and Akito Arima.