MnO and Ba-doped MnO NPs were prepared through the chemical reduction method and these NPs were used for the photodegradation of Methylene blue dye (MB) dye in an aqueous medium. The morphological study shows that the MnO NPs have granular shapes while Ba-doped MnO NPs have irregular spherical shapes. XRD results presented that the diameter of MnO and Ba-doped MnO NPs was 30 and 36 nm, respectively. FTIR spectra show peaks in the range of 750–1385 cm−1, which present the metal oxide NPs. The photocatalytic degradation study demonstrated that the MnO and Ba-doped MnO NPs degraded about 73 and 86% dye within 250 min, respectively. The effect of various parameters like pH, initial dye concentration, and catalyst dosage on the photodegradation of dye was also studied. The recovered MnO and Ba-doped MnO NPs also significantly degraded the Methylene Blue dye in aqueous media.