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In this study, barium-doped lanthanum manganite, La0.8Ba0.2MnO3 was synthesized via a mechano-thermal route employing high energy ball milling followed by heat treatment. The structural evolution, morphology and thermal behavior of the powders were evaluated using X-ray diffraction, high resolution scanning electron microscope, and differential thermal analysis/thermo-gravimetric analysis, respectively. The magnetic properties were investigated using an AC susceptometer. X-ray diffraction results revealed the formation of a single phase La0.8Ba0.2MnO3 perovskite with a mean crystallite size of 13nm in a 30h milled sample after the heat treatment at 700°C for 1h. The images of the high resolution scanning electron microscope showed the mean particle size of 350nm for 5h heat treated sample at 1200°C and a change from round-type to multifaceted morphology by increasing the heat treatment temperature. AC susceptibility results showed that increasing heat treatment temperature and time to 1300°C and 5h, respectively, leads to 60% increase in Curie temperature. The paramagnetic–ferromagnetic transition width decreases by increasing the heat treatment temperature and time. The samples heat treated at 900 and 1100°C for 1h exhibited reentered spin-glass behavior which is probably because of the deficiency of Ba content. The milled sample after the heat treatment at 1300°C exhibits metal–insulator behavior and metal–insulator transition temperature (TM–I) is highly dependent on the applied magnetic field. The maximum TM–I shifts from 230K at zero magnetic field towards room temperature near 244K with applying the external magnetic field of 10kOe. It was found that the milled sample after heat treatment at 1300°C exhibits the high MR of 18% at 300K under H=10kOe. This exceptional MR at room temperature suggests this material as a most promising nano-structured CMR material. [ABSTRACT FROM AUTHOR]