A novel methodology is proposed for damage identification of frame structures based on changes in modal parameters such as natural frequency, mode shape using Extended Improved Particle Swarm Optimization (EIPSO) technique. A finite element code is developed to model a single bay portal frame structure in MATLAB based on Timoshenko beam theory and to obtain the free vibration response. Modal parameters of single bay portal frame structure are also obtained from experimental analysis adopting roving hammer test and shaker test using PULSE Lab Shop of Brüel & Kjær (B&K) make for validation of the numerical model. Subsequently, structural damages in terms of local variations of stiffness/mass are introduced in the numerically developed single bay portal frame structure and the EIPSO algorithm is employed for exact identification of location and the magnitude of damage by optimizing the objective function which is formulated using mode shapes and the natural frequencies obtained from damaged and undamaged portal frame structure. The validity and usefulness of the proposed method are illustrated with obtained results of portal frame structure. The illustrated results show the proposed method is effective for identification of structural damage as well as in the SHM field.