: Extremely low cycle fatigue (ELCF) is a cyclic loading in which loads are larg and strain control, strains are in plastic area and high above the yield point. Speciman life is less than 1000 cycles (in some defenitions less than 100 cycles). Because extremely low cycle fatigue is a relatively new topic, in this research ELCF of dual phase steel sheet was investigated. In this thesis, investigation was carried out from two perspectives: experimental and finite element simulation in order to obtain a suitable material model (elastic-plastic and damage model) for predicting extremely low cycle fatigue (ELCF) in dual phase steel to determine hysterzis diagram, life-strain diagram and damage initiation and propagation mechanisms and compare them with the experiment. Experiments included standard tensile tests to measure mechanical properties and material parameters and ELCF tests to achieve the specimen life, hysterzis and life-strain diagrams. By performing a uniaxial tensile test, the main properties of the material used in this thesis were determined as follows: yield stress 382 MPa, ultimate strength 648 MPa and elongation of 30%. Extremely low cycle fatigue tests were performed for displacement ±0.22 to ±0.4 mm and the average of the tests performed, showed that the fatigue life of the samples varies from 198 to 1999 cycles. After that, fracture surface of test specimens were investigated for damage mechanism with scanning electron microscopy (SEM). Simulation was performed in ABAQUS software by writing a user subroutine (VUMAT). In this way, after choosing an appropriate representative volume element (RVE), hardening behavior of martensite phase was defined by means of Rodrigues equations and a combined hardening coupled with modified Lemaitre damage model was used for ferrite phase defined in VUMAT code while loading and meshing were defined on a 2D plane strain model. For verification of the modelling several RVEs were chosen and simulated. At the end, the life-strain and the hysterzis diagrams and damage mechanisms that were obtained from the simulation were compared with experimental results. It was done for the selected representative volume element with dimensions of 25 × 25 ?m 2 . Very good matching of simulation and experimental results was observed with an error of less than 5%. Keyword: dual phase steel, combined hardening, modified Lemaitre damage model, exteremely low cycle fatigue, damage and fracture mechanism. :