La1-xSrx FeO3-δ systems were investigated by low-frequency internal friction method. The results show that the curves of the internal friction and modulus versus temperature vary with the Sr-dopant content （x）. For the undoped sample，no obvious change on the internal friction and modulus curves was observed between -150—380℃，but the samples with x=0.25，1/3，0.5 and 0.6 show an intenal friction peak P1 with the feature of phase transitions，and the peak temperature moves toward lower temperature with incresing Sr content. This peak was suggested to be associated with a phase transition from rhombohedral to orthorhombic. The samples with x=0.25，1/3，0.5，0.6 and 2/3 show a relaxation type peak P2 accompanied by a decrease in modulus，which can be attributed to the motion of domain walls whose mobility was contolled by the diffusion of oxygen vacancies. The samples with x=0.5，0.6 and 2/3 show a rapid change in the curves of modulus versus temperature，which is related to a ferroelastic phase transition from rhombohedral to cubic.