Optimization of Advanced Oxidation Processes (AOPs) is key for the demand in green and sustainable method for degradation of organic contaminants in aqueous solution. In this study, the effect of Cr doping on CeO2 nanostructure was investigated to evaluate the catalytic performances of the Cr doped CeO2 nanocomposites with Methylene Blue (MB) used as model contaminant. Two types of AOPs were also explored; photocatalysis and H2O2 assisted. The Cr-doped CeO2 samples were prepared by deposition precipitation method and characterized with XRD, FE-SEM-EDX, UV-vis Spectroscopy and TPR. Generally, increase in Cr doping improved the catalytic activity in MB degradation efficiency for photocatalysis and H2O2-assisted methods, where with 3% weight of Crdoping achieved 41 % and 59 % of MB degradation across 100 min respectively. The improvement of catalytic activity was attributed to the effects on Cr doping, which lowers the CeO2 band gap and also the Cr species serving as electron trapping centers to slow down the recombination of the charge carriers. The MB degradation results also showed that for Cr-doped CeO2 system, H2O2-assisted was the more effective catalytic method compared to photocatalysis. Isopropanol has been found explicitly feasible to demonstrate a plausible scavenging properties toward hydroxyl radical by suppressing the MB degradation in the reaction media, thus, suggesting that, the MB degradation mechanism proceeds via hydroxyl radical species.