The Perovskite BaFeO3 nano-powder has been synthesized by sol-gel method. The micro-structure and morphology of BaFeO3 nano-powder have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The results showed that the samples annealed at 800 ℃ formed the perovskite-type BaFeO3 with grain size of about 20 nm and the (110) and (100) spacings of about 0.280 nm and 0.401 nm, respectively. The room temperature magnetic properties of samples have been measured on vibrating sample magnetometer (VSM). It is shown that the BaFeO3 nano-powder has a complete hysteresis loop, which means that BaFeO3 powder possess significant weak ferromagnetism at room temperature, and this property changes obviously with the annealing temperature. Ferromagnetism of perovskite BaFeO3 nano-powder mainly originates from oxygen vacancy among Fe3+-O-Fe4+.