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Effects of oxygen deficiency on the magnetic and transport properties of La2/3Ba1/3MnO3-δ polycrystalline perovskites have been investigated. As the nonstoichiometry parameter δ increases from 0.00 to 0.10, the lattice parameters at room temperature increase from 3.892(3) A to 3.909(3) A, the resistivity increases and the ferromagnetic ordering transition temperature shifts from 337K to 268 K. A large magnetoresistance effect with -Aρ/ρ0 of about 30%(955 kA/m, δ = 0.10) and a large magnetic entropy change of about 2.7 J/kg.K (796kA/m, δ = 0.00)is obtained in polycrystalline La2/3Ba1/3MnO3-δ. The enhanced magnetoresistance effect at low temperature would be related to the grain boundaries of the polycrystalline samples.