The effect of particle size distribution on the field and temperature dependence of the hysteresis loop features like coercivity(HC),remanence(MR),and blocking temperature(TB)is simulated for an ensemble of single domain ferro-magnetic nanoparticles with uniaxial anisotropy.Our simulations are based on the two-state model for TTB.It is found that the increase in the grain size significantly enhances HC and TB.The presence of interparticle exchange interaction in the system suppresses HC but causes MR to significantly increase.Our results show that the parameters associated with the particle size distribution(Dd,δ)such as the mean particle size d and standard-deviation δ play key roles in the magnetic behavior of the system.