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Recently, the IRT with covariate (IRT-C) approach was developed for DIF detection (Tay, Huang, & Vermunt, 2016). However, many large-scale educational assessment data sets commonly have multilevel structures. Because ignoring the multilevel structure in data analyses may compromise the parameter estimation, applying the single-level IRT-C to large-scale educational assessments with multilevel structures may result in erroneous DIF detection. Therefore, the purpose of this study is to expand the IRT-C model in DIF detection to account for the multilevel structure of Programme for International Student Assessment (PISA) 2006 Math data using a Bayesian approach. The results of the study demonstrated the utility of the multilevel IRT-C models to detect DIF items for large-scale assessment data, accounting for cross-county differences.