Oil shale ash (OSA) is a solid waste from the production process of shale oil. The large quantity of OSA generated in China yearly has led to serious, difficult-to-solve environmental problems. With a view to reducing OSA-induced environmental pressure, in this study, removal of methylene blue (MB) from aqueous solution by using OSA was investigated at different physical and chemical parameters, such as pH, temperature, initial MB concentration, and contact time. The experimental results showed that both the Langmuir and Freundlich models fitted the MB adsorption data well with an adsorption capacity as high as 250 mg/g. Removal of MB by OSA was relatively fast and equilibrium could be achieved in 2 h. Adsorption of MB by OSA was an endothermic reaction, and the change of free energy after MB adsorption indicated physical adsorption in nature. The results suggest a new potential utilization of OSA for the removal of color dye from wastewater.