Accurate quantification of liver fat content is needed for early detection, staging, and treatment monitoring of non-alcoholic fatty liver disease. Chemical shift encoded MRI techniques enable accurate fat quantification though proton density fat fraction maps. CT is capable of quantifying fat based on the decrease in attenuation with increasing liver fat concentration. Current MR quantitative fat phantoms do not accurately mimic CT-based attenuation in the presence of liver fat. Therefore, the purpose of this work was to develop and validate the performance of a novel multimodality phantom that mimics the signals of liver fat in both MRI and CT.